diff --git a/common/fips202.c b/common/fips202.c
index 66e97ae2..d61c28fd 100644
--- a/common/fips202.c
+++ b/common/fips202.c
@@ -402,6 +402,157 @@ static void keccak_squeezeblocks(uint8_t *h, size_t nblocks,
     }
 }
 
+/*************************************************
+ * Name:        keccak_inc_init
+ *
+ * Description: Initializes the incremental Keccak state to zero.
+ *
+ * Arguments:   - uint64_t *s_inc: pointer to input/output incremental state
+ *                First 25 values represent Keccak state.
+ *                26th value represents either the number of absorbed bytes
+ *                that have not been permuted, or not-yet-squeezed bytes.
+ **************************************************/
+static void keccak_inc_init(uint64_t *s_inc) {
+    size_t i;
+
+    for (i = 0; i < 25; ++i) {
+        s_inc[i] = 0;
+    }
+    s_inc[25] = 0;
+}
+
+/*************************************************
+ * Name:        keccak_inc_absorb
+ *
+ * Description: Incremental keccak absorb
+ *              Preceded by keccak_inc_init, succeeded by keccak_inc_finalize
+ *
+ * Arguments:   - uint64_t *s_inc: pointer to input/output incremental state
+ *                First 25 values represent Keccak state.
+ *                26th value represents either the number of absorbed bytes
+ *                that have not been permuted, or not-yet-squeezed bytes.
+ *              - uint32_t r: rate in bytes (e.g., 168 for SHAKE128)
+ *              - const uint8_t *m: pointer to input to be absorbed into s
+ *              - size_t mlen: length of input in bytes
+ **************************************************/
+static void keccak_inc_absorb(uint64_t *s_inc, uint32_t r, const uint8_t *m,
+                              size_t mlen) {
+    size_t i;
+
+    /* Recall that s_inc[25] is the non-absorbed bytes xored into the state */
+    while (mlen + s_inc[25] >= r) {
+        for (i = 0; i < r - s_inc[25]; i++) {
+            /* Take the i'th byte from message
+               xor with the s_inc[25] + i'th byte of the state; little-endian */
+            s_inc[(s_inc[25] + i) >> 3] ^= (uint64_t)m[i] << (8 * ((s_inc[25] + i) & 0x07));
+        }
+        mlen -= (size_t)(r - s_inc[25]);
+        m += r - s_inc[25];
+        s_inc[25] = 0;
+
+        KeccakF1600_StatePermute(s_inc);
+    }
+
+    for (i = 0; i < mlen; i++) {
+        s_inc[(s_inc[25] + i) >> 3] ^= (uint64_t)m[i] << (8 * ((s_inc[25] + i) & 0x07));
+    }
+    s_inc[25] += mlen;
+}
+
+/*************************************************
+ * Name:        keccak_inc_finalize
+ *
+ * Description: Finalizes Keccak absorb phase, prepares for squeezing
+ *
+ * Arguments:   - uint64_t *s_inc: pointer to input/output incremental state
+ *                First 25 values represent Keccak state.
+ *                26th value represents either the number of absorbed bytes
+ *                that have not been permuted, or not-yet-squeezed bytes.
+ *              - uint32_t r: rate in bytes (e.g., 168 for SHAKE128)
+ *              - uint8_t p: domain-separation byte for different
+ *                                 Keccak-derived functions
+ **************************************************/
+static void keccak_inc_finalize(uint64_t *s_inc, uint32_t r, uint8_t p) {
+    /* After keccak_inc_absorb, we are guaranteed that s_inc[25] < r,
+       so we can always use one more byte for p in the current state. */
+    s_inc[s_inc[25] >> 3] ^= (uint64_t)p << (8 * (s_inc[25] & 0x07));
+    s_inc[(r - 1) >> 3] ^= (uint64_t)128 << (8 * ((r - 1) & 0x07));
+    s_inc[25] = 0;
+}
+
+/*************************************************
+ * Name:        keccak_inc_squeeze
+ *
+ * Description: Incremental Keccak squeeze; can be called on byte-level
+ *
+ * Arguments:   - uint8_t *h: pointer to output bytes
+ *              - size_t outlen: number of bytes to be squeezed
+ *              - uint64_t *s_inc: pointer to input/output incremental state
+ *                First 25 values represent Keccak state.
+ *                26th value represents either the number of absorbed bytes
+ *                that have not been permuted, or not-yet-squeezed bytes.
+ *              - uint32_t r: rate in bytes (e.g., 168 for SHAKE128)
+ **************************************************/
+static void keccak_inc_squeeze(uint8_t *h, size_t outlen,
+                               uint64_t *s_inc, uint32_t r) {
+    size_t i;
+
+    /* First consume any bytes we still have sitting around */
+    for (i = 0; i < outlen && i < s_inc[25]; i++) {
+        /* There are s_inc[25] bytes left, so r - s_inc[25] is the first
+           available byte. We consume from there, i.e., up to r. */
+        h[i] = (uint8_t)(s_inc[(r - s_inc[25] + i) >> 3] >> (8 * ((r - s_inc[25] + i) & 0x07)));
+    }
+    h += i;
+    outlen -= i;
+    s_inc[25] -= i;
+
+    /* Then squeeze the remaining necessary blocks */
+    while (outlen > 0) {
+        KeccakF1600_StatePermute(s_inc);
+
+        for (i = 0; i < outlen && i < r; i++) {
+            h[i] = (uint8_t)(s_inc[i >> 3] >> (8 * (i & 0x07)));
+        }
+        h += i;
+        outlen -= i;
+        s_inc[25] = r - i;
+    }
+}
+
+void shake128_inc_init(uint64_t *s_inc) {
+    keccak_inc_init(s_inc);
+}
+
+void shake128_inc_absorb(uint64_t *s_inc, const uint8_t *input, size_t inlen) {
+    keccak_inc_absorb(s_inc, SHAKE128_RATE, input, inlen);
+}
+
+void shake128_inc_finalize(uint64_t *s_inc) {
+    keccak_inc_finalize(s_inc, SHAKE128_RATE, 0x1F);
+}
+
+void shake128_inc_squeeze(uint8_t *output, size_t outlen, uint64_t *s_inc) {
+    keccak_inc_squeeze(output, outlen, s_inc, SHAKE128_RATE);
+}
+
+void shake256_inc_init(uint64_t *s_inc) {
+    keccak_inc_init(s_inc);
+}
+
+void shake256_inc_absorb(uint64_t *s_inc, const uint8_t *input, size_t inlen) {
+    keccak_inc_absorb(s_inc, SHAKE256_RATE, input, inlen);
+}
+
+void shake256_inc_finalize(uint64_t *s_inc) {
+    keccak_inc_finalize(s_inc, SHAKE256_RATE, 0x1F);
+}
+
+void shake256_inc_squeeze(uint8_t *output, size_t outlen, uint64_t *s_inc) {
+    keccak_inc_squeeze(output, outlen, s_inc, SHAKE256_RATE);
+}
+
+
 /*************************************************
  * Name:        shake128_absorb
  *
diff --git a/common/fips202.h b/common/fips202.h
index bcd5aa96..4a28d67b 100644
--- a/common/fips202.h
+++ b/common/fips202.h
@@ -13,10 +13,19 @@ void shake128_absorb(uint64_t *s, const uint8_t *input, size_t inlen);
 
 void shake128_squeezeblocks(uint8_t *output, size_t nblocks, uint64_t *s);
 
-void shake256_absorb(uint64_t *s, const uint8_t *input, size_t inlen);
+void shake128_inc_init(uint64_t *s_inc);
+void shake128_inc_absorb(uint64_t *s_inc, const uint8_t *input, size_t inlen);
+void shake128_inc_finalize(uint64_t *s_inc);
+void shake128_inc_squeeze(uint8_t *output, size_t outlen, uint64_t *s_inc);
 
+void shake256_absorb(uint64_t *s, const uint8_t *input, size_t inlen);
 void shake256_squeezeblocks(uint8_t *output, size_t nblocks, uint64_t *s);
 
+void shake256_inc_init(uint64_t *s_inc);
+void shake256_inc_absorb(uint64_t *s_inc, const uint8_t *input, size_t inlen);
+void shake256_inc_finalize(uint64_t *s_inc);
+void shake256_inc_squeeze(uint8_t *output, size_t outlen, uint64_t *s_inc);
+
 void shake128(uint8_t *output, size_t outlen,
               const uint8_t *input, size_t inlen);
 
diff --git a/test/Makefile b/test/Makefile
index 5d184dff..0557b48e 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -17,7 +17,7 @@ DEST_DIR=../bin
 # This -Wall was supported by the European Commission through the ERC Starting Grant 805031 (EPOQUE)
 CFLAGS=-Wall -Wextra -Wpedantic -Werror -std=c99 -I$(COMMON_DIR) $(EXTRAFLAGS)
 
-all: $(DEST_DIR)/functest_$(SCHEME)_$(IMPLEMENTATION) $(DEST_DIR)/testvectors_$(SCHEME)_$(IMPLEMENTATION)
+all: $(DEST_DIR)/functest_$(SCHEME)_$(IMPLEMENTATION) $(DEST_DIR)/testvectors_$(SCHEME)_$(IMPLEMENTATION) $(DEST_DIR)/test_fips202
 
 .PHONY: build-scheme
 build-scheme:
@@ -33,6 +33,10 @@ functest: $(DEST_DIR)/functest_$(SCHEME)_$(IMPLEMENTATION)
 .PHONY: testvectors
 testvectors: $(DEST_DIR)/testvectors_$(SCHEME)_$(IMPLEMENTATION)
 
+$(DEST_DIR)/test_fips202: common/fips202.c $(COMMON_FILES)
+	mkdir -p $(DEST_DIR)
+	$(CC) $(CFLAGS) $< $(COMMON_FILES) -o $@
+
 $(DEST_DIR)/functest_$(SCHEME)_$(IMPLEMENTATION): build-scheme crypto_$(TYPE)/functest.c $(COMMON_FILES) $(COMMON_DIR)/randombytes.c $(COMMON_HEADERS)
 	mkdir -p $(DEST_DIR)
 	$(CC) $(CFLAGS) -DPQCLEAN_NAMESPACE=PQCLEAN_$(SCHEME_UPPERCASE)_$(IMPLEMENTATION_UPPERCASE) -I$(SCHEME_DIR) crypto_$(TYPE)/functest.c $(COMMON_FILES) $(COMMON_DIR)/notrandombytes.c -o $@ -L$(SCHEME_DIR) -l$(SCHEME)_$(IMPLEMENTATION)
@@ -45,3 +49,4 @@ $(DEST_DIR)/testvectors_$(SCHEME)_$(IMPLEMENTATION): build-scheme crypto_$(TYPE)
 clean:
 	$(RM) $(DEST_DIR)/functest_$(SCHEME)_$(IMPLEMENTATION)
 	$(RM) $(DEST_DIR)/testvectors_$(SCHEME)_$(IMPLEMENTATION)
+	$(RM) $(DEST_DIR)/test_fips202
diff --git a/test/common/fips202.c b/test/common/fips202.c
new file mode 100644
index 00000000..e559d07f
--- /dev/null
+++ b/test/common/fips202.c
@@ -0,0 +1,236 @@
+#include "fips202.h"
+
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <inttypes.h>
+
+const unsigned char plaintext[44] = "The quick brown fox jumps over the lazy dog";
+const unsigned char expected[512] = {
+    0xf4, 0x20, 0x2e, 0x3c, 0x58, 0x52, 0xf9, 0x18, 0x2a, 0x04, 0x30, 0xfd,
+    0x81, 0x44, 0xf0, 0xa7, 0x4b, 0x95, 0xe7, 0x41, 0x7e, 0xca, 0xe1, 0x7d,
+    0xb0, 0xf8, 0xcf, 0xee, 0xd0, 0xe3, 0xe6, 0x6e, 0xb5, 0x58, 0x5e, 0xc6,
+    0xf8, 0x60, 0x21, 0xca, 0xcf, 0x27, 0x2c, 0x79, 0x8b, 0xcf, 0x97, 0xd3,
+    0x68, 0xb8, 0x86, 0xb1, 0x8f, 0xec, 0x3a, 0x57, 0x1f, 0x09, 0x60, 0x86,
+    0xa5, 0x23, 0x71, 0x7a, 0x37, 0x32, 0xd5, 0x0d, 0xb2, 0xb0, 0xb7, 0x99,
+    0x8b, 0x41, 0x17, 0xae, 0x66, 0xa7, 0x61, 0xcc, 0xf1, 0x84, 0x7a, 0x16,
+    0x16, 0xf4, 0xc0, 0x7d, 0x51, 0x78, 0xd0, 0xd9, 0x65, 0xf9, 0xfe, 0xba,
+    0x35, 0x14, 0x20, 0xf8, 0xbf, 0xb6, 0xf5, 0xab, 0x9a, 0x0c, 0xb1, 0x02,
+    0x56, 0x8e, 0xab, 0xf3, 0xdf, 0xa4, 0xe2, 0x22, 0x79, 0xf8, 0x08, 0x2d,
+    0xce, 0x81, 0x43, 0xeb, 0x78, 0x23, 0x5a, 0x1a, 0x54, 0x91, 0x4a, 0xb7,
+    0x1a, 0xbb, 0x07, 0xf2, 0xf3, 0x64, 0x84, 0x68, 0x37, 0x0b, 0x9f, 0xbb,
+    0x07, 0x1e, 0x07, 0x4f, 0x1c, 0x03, 0x0a, 0x40, 0x30, 0x22, 0x5f, 0x40,
+    0xc3, 0x94, 0x80, 0x33, 0x9f, 0x3d, 0xc7, 0x1d, 0x0f, 0x04, 0xf7, 0x13,
+    0x26, 0xde, 0x13, 0x81, 0x67, 0x4c, 0xc8, 0x9e, 0x25, 0x9e, 0x21, 0x99,
+    0x27, 0xfa, 0xe8, 0xea, 0x27, 0x99, 0xa0, 0x3d, 0xa8, 0x62, 0xa5, 0x5a,
+    0xfa, 0xfe, 0x67, 0x09, 0x57, 0xa2, 0xaf, 0x33, 0x18, 0xd9, 0x19, 0xd0,
+    0xa3, 0x35, 0x8f, 0x3b, 0x89, 0x12, 0x36, 0xd6, 0xa8, 0xe8, 0xd1, 0x99,
+    0x99, 0xd1, 0x07, 0x6b, 0x52, 0x99, 0x68, 0xfa, 0xef, 0xbd, 0x88, 0x0d,
+    0x77, 0xbb, 0x30, 0x08, 0x29, 0xdc, 0xa8, 0x7e, 0x9c, 0x8e, 0x4c, 0x28,
+    0xe0, 0x80, 0x0f, 0xf3, 0x74, 0x90, 0xa5, 0xbd, 0x8c, 0x36, 0xc0, 0xb0,
+    0xbd, 0xb2, 0x70, 0x1a, 0x5d, 0x58, 0xd0, 0x33, 0x78, 0xb9, 0xdb, 0xd3,
+    0x84, 0x38, 0x9e, 0x3e, 0xf0, 0xfd, 0x40, 0x03, 0xb0, 0x89, 0x98, 0xfd,
+    0x3f, 0x32, 0xfe, 0x1a, 0x08, 0x10, 0xfc, 0x0e, 0xcc, 0xaa, 0xd9, 0x4b,
+    0xca, 0x8d, 0xd8, 0x3b, 0x34, 0x55, 0x9c, 0x33, 0x3f, 0x0b, 0x16, 0xdf,
+    0xc2, 0x89, 0x6e, 0xd8, 0x7b, 0x30, 0xba, 0x14, 0xc8, 0x1f, 0x87, 0xcd,
+    0x8b, 0x4b, 0xb6, 0x31, 0x7d, 0xb8, 0x9b, 0x0e, 0x7e, 0x94, 0xc0, 0x61,
+    0x6f, 0x9a, 0x66, 0x5f, 0xba, 0x5b, 0x0e, 0x6f, 0xb3, 0x54, 0x9c, 0x9d,
+    0x7b, 0x68, 0xe6, 0x6d, 0x08, 0xa8, 0x6e, 0xb2, 0xfa, 0xec, 0x05, 0xcc,
+    0x46, 0x2a, 0x77, 0x18, 0x06, 0xb9, 0x3c, 0xc3, 0x8b, 0x0a, 0x4f, 0xeb,
+    0x99, 0x35, 0xc6, 0xc8, 0x94, 0x5d, 0xa6, 0xa5, 0x89, 0x89, 0x1b, 0xa5,
+    0xee, 0x99, 0x75, 0x3c, 0xfd, 0xd3, 0x8e, 0x1a, 0xbc, 0x71, 0x47, 0xfd,
+    0x74, 0xb7, 0xc7, 0xd1, 0xce, 0x06, 0x09, 0xb6, 0x68, 0x0a, 0x2e, 0x18,
+    0x88, 0x8d, 0x84, 0x94, 0x9b, 0x6e, 0x6c, 0xf6, 0xa2, 0xaa, 0x41, 0x13,
+    0x53, 0x5a, 0xae, 0xe0, 0x79, 0x45, 0x9e, 0x3f, 0x25, 0x7b, 0x56, 0x9a,
+    0x94, 0x50, 0x52, 0x3c, 0x41, 0xf5, 0xb5, 0xba, 0x4b, 0x79, 0xb3, 0xba,
+    0x59, 0x49, 0x14, 0x0a, 0x74, 0xbb, 0x04, 0x8d, 0xe0, 0x65, 0x7d, 0x04,
+    0x95, 0x4b, 0xdd, 0x71, 0xda, 0xe7, 0x6f, 0x61, 0xe2, 0xa1, 0xf8, 0x8a,
+    0xec, 0xb9, 0x1c, 0xfa, 0x5b, 0x36, 0xc1, 0xbf, 0x33, 0x50, 0xa7, 0x98,
+    0xdc, 0x4d, 0xcf, 0x48, 0x62, 0x8e, 0xff, 0xe3, 0xa0, 0xc5, 0x34, 0x0c,
+    0x75, 0x6b, 0xd9, 0x22, 0xf7, 0x8d, 0x0e, 0x36, 0xef, 0x7d, 0xf1, 0x2c,
+    0xe7, 0x8c, 0x17, 0x9c, 0xc7, 0x21, 0xad, 0x08, 0x7e, 0x15, 0xea, 0x49,
+    0x6b, 0xf5, 0xf6, 0x0b, 0x21, 0xb5, 0x82, 0x2d
+};
+
+static int test_shake128_incremental(void) {
+    unsigned char input[512];
+    unsigned char check[512];
+    unsigned char output[512];
+    uint64_t s_inc_absorb[26];
+    uint64_t s_inc_squeeze[26];
+    uint64_t s_inc_squeeze_all[26];
+    uint64_t s_inc_both[26];
+    uint64_t s_combined[25];
+    int i;
+    int absorbed;
+    int squeezed;
+    int returncode = 0;
+
+    for (i = 0; i < 512; i++) {
+        input[i] = i;
+    }
+
+    shake128(check, 512, input, 512);
+
+    shake128_inc_init(s_inc_absorb);
+
+    absorbed = 0;
+    for (i = 0; i < 512 && absorbed + i <= 512; i++) {
+        shake128_inc_absorb(s_inc_absorb, input + absorbed, i);
+        absorbed += i;
+    }
+    shake128_inc_absorb(s_inc_absorb, input + absorbed, 512 - absorbed);
+
+    shake128_inc_finalize(s_inc_absorb);
+
+    shake128_absorb(s_combined, input, 512);
+
+    if (memcmp(s_inc_absorb, s_combined, 25 * sizeof(uint64_t))) {
+        printf("ERROR shake128 state after incremental absorb did not match all-at-once absorb.\n");
+        printf("  Expected: ");
+        for (i = 0; i < 25; i++) {
+            printf("%016" PRIx64, s_combined[i]);
+        }
+        printf("\n");
+        printf("  State:    ");
+        for (i = 0; i < 25; i++) {
+            printf("%016" PRIx64, s_inc_absorb[i]);
+        }
+        printf("\n");
+        for (i = 0; i < 8 * 25; i++) {
+            if (((s_combined[i >> 3]   >> (8*(i & 0x7))) & 0xFF) !=
+                ((s_inc_absorb[i >> 3] >> (8*(i & 0x7))) & 0xFF)) {
+                printf("  First occurred in int %d, byte %d (%02X should be %02X)\n",
+                    i >> 3, i & 0x7,
+                    (uint8_t)((s_inc_absorb[i >> 3] >> (8*(i & 0x7))) & 0xFF),
+                    (uint8_t)((s_combined[i >> 3]   >> (8*(i & 0x7))) & 0xFF));
+                break;
+            }
+        }
+        returncode = 1;
+    }
+
+    memcpy(s_inc_both, s_inc_absorb, 26 * sizeof(uint64_t));
+
+    shake128_squeezeblocks(output, 3, s_inc_absorb);
+
+    if (memcmp(check, output, 3*SHAKE128_RATE)) {
+        printf("ERROR shake128 incremental absorb did not match shake128.\n");
+        printf("  Expected: ");
+        for (i = 0; i < 3*SHAKE128_RATE; i++) {
+            printf("%02X", check[i]);
+        }
+        printf("\n");
+        printf("  Received: ");
+        for (i = 0; i < 3*SHAKE128_RATE; i++) {
+            printf("%02X", output[i]);
+        }
+        printf("\n");
+        returncode = 1;
+    }
+
+    shake128_absorb(s_inc_squeeze, input, 512);
+    s_inc_squeeze[25] = 0;
+
+    memcpy(s_inc_squeeze_all, s_inc_squeeze, 26 * sizeof(uint64_t));
+
+    shake128_inc_squeeze(output, 512, s_inc_squeeze_all);
+
+    if (memcmp(check, output, 512)) {
+        printf("ERROR shake128 incremental squeeze-all did not match shake128.\n");
+        printf("  Expected: ");
+        for (i = 0; i < 512; i++) {
+            printf("%02X", check[i]);
+        }
+        printf("\n");
+        printf("  Received: ");
+        for (i = 0; i < 512; i++) {
+            printf("%02X", output[i]);
+        }
+        printf("\n");
+        returncode = 1;
+    }
+
+    squeezed = 0;
+    memset(output, 0, 512);
+    for (i = 0; i < 512 && squeezed + i <= 512; i++) {
+        shake128_inc_squeeze(output + squeezed, i, s_inc_squeeze);
+        squeezed += i;
+    }
+    shake128_inc_squeeze(output + squeezed, 512 - squeezed, s_inc_squeeze);
+
+    if (memcmp(check, output, 512)) {
+        printf("ERROR shake128 incremental squeeze did not match shake128.\n");
+        printf("  Expected: ");
+        for (i = 0; i < 512; i++) {
+            printf("%02X", check[i]);
+        }
+        printf("\n");
+        printf("  Received: ");
+        for (i = 0; i < 512; i++) {
+            printf("%02X", output[i]);
+        }
+        printf("\n");
+        returncode = 1;
+    }
+
+    squeezed = 0;
+    memset(output, 0, 512);
+    for (i = 0; i < 512 && squeezed + i <= 512; i++) {
+        shake128_inc_squeeze(output + squeezed, i, s_inc_both);
+        squeezed += i;
+    }
+    shake128_inc_squeeze(output + squeezed, 512 - squeezed, s_inc_both);
+
+    if (memcmp(check, output, 512)) {
+        printf("ERROR shake128 incremental absorb + squeeze did not match shake128.\n");
+        printf("  Expected: ");
+        for (i = 0; i < 512; i++) {
+            printf("%02X", check[i]);
+        }
+        printf("\n");
+        printf("  Received: ");
+        for (i = 0; i < 512; i++) {
+            printf("%02X", output[i]);
+        }
+        printf("\n");
+        returncode = 1;
+    }
+
+    return returncode;
+}
+
+static int test_shake128(void) {
+    unsigned char output[32];
+    int i = 0;
+
+    shake128(output, 32, plaintext, 43);
+
+    if (memcmp(expected, output, 32)) {
+        printf("ERROR shake128 output did not match test vector.\n");
+        printf("Expected: ");
+        for (i = 0; i < 32; i++) {
+            printf("%02X", expected[i]);
+        }
+        printf("\n");
+        printf("Received: ");
+        for (i = 0; i < 32; i++) {
+            printf("%02X", output[i]);
+        }
+        printf("\n");
+        return 1;
+    }
+
+    return 0;
+}
+
+int main(void) {
+    int result = 0;
+    result += test_shake128();
+    result += test_shake128_incremental();
+
+    if (result != 0) {
+        puts("Errors occurred");
+    }
+    return result;
+}