diff --git a/include/gmssl/sm3.h b/include/gmssl/sm3.h
index 9b9be2b0..37d18cc4 100644
--- a/include/gmssl/sm3.h
+++ b/include/gmssl/sm3.h
@@ -58,6 +58,7 @@ void sm3_update(SM3_CTX *ctx, const uint8_t *data, size_t datalen);
 void sm3_finish(SM3_CTX *ctx, uint8_t dgst[SM3_DIGEST_SIZE]);
 void sm3_digest(const uint8_t *data, size_t datalen, uint8_t dgst[SM3_DIGEST_SIZE]);
 
+void sm3_compress_blocks(uint32_t digest[8], const uint8_t *data, size_t blocks);
 
 typedef struct {
 	SM3_CTX sm3_ctx;
diff --git a/src/sm3.c b/src/sm3.c
index 1853b62c..eb2d2e64 100644
--- a/src/sm3.c
+++ b/src/sm3.c
@@ -294,7 +294,6 @@ void sm3_compress_blocks(uint32_t digest[8], const uint8_t *data, size_t blocks)
 	}
 }
 
-
 void sm3_init(SM3_CTX *ctx)
 {
 	memset(ctx, 0, sizeof(*ctx));
@@ -321,7 +320,6 @@ void sm3_update(SM3_CTX *ctx, const uint8_t *data, size_t data_len)
 			ctx->num += data_len;
 			return;
 		} else {
-			memcpy(ctx->block + ctx->num, data, left);
 			sm3_compress_blocks(ctx->digest, ctx->block, 1);
 			ctx->nblocks++;
 			data += left;
@@ -330,10 +328,12 @@ void sm3_update(SM3_CTX *ctx, const uint8_t *data, size_t data_len)
 	}
 
 	blocks = data_len / SM3_BLOCK_SIZE;
-	sm3_compress_blocks(ctx->digest, data, blocks);
-	ctx->nblocks += blocks;
-	data += SM3_BLOCK_SIZE * blocks;
-	data_len -= SM3_BLOCK_SIZE * blocks;
+	if (blocks) {
+		sm3_compress_blocks(ctx->digest, data, blocks);
+		ctx->nblocks += blocks;
+		data += SM3_BLOCK_SIZE * blocks;
+		data_len -= SM3_BLOCK_SIZE * blocks;
+	}
 
 	ctx->num = data_len;
 	if (data_len) {