diff --git a/tests/suites/test_suite_chachapoly.data b/tests/suites/test_suite_chachapoly.data
index b0eedea..34cb568 100644
--- a/tests/suites/test_suite_chachapoly.data
+++ b/tests/suites/test_suite_chachapoly.data
@@ -16,6 +16,9 @@
 ChaCha20-Poly1305 RFC 7539 Test Vector #1 (Decrypt, not authentic)
 mbedtls_chachapoly_dec:"1c9240a5eb55d38af333888604f6b5f0473917c1402b80099dca5cbc207075c0":"000000000102030405060708":"f33388860000000000004e91":"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":"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":"fead9d67890cbb22392336fea1851f38":MBEDTLS_ERR_CHACHAPOLY_AUTH_FAILED
 
+ChaCha20-Poly1305 State Flow
+chachapoly_state:
+
 ChaCha20-Poly1305 Parameter Validation
 chachapoly_bad_params:
 
diff --git a/tests/suites/test_suite_chachapoly.function b/tests/suites/test_suite_chachapoly.function
index 3f8145a..e379309 100644
--- a/tests/suites/test_suite_chachapoly.function
+++ b/tests/suites/test_suite_chachapoly.function
@@ -268,6 +268,86 @@
 }
 /* END_CASE */
 
+/* BEGIN_CASE */
+void chachapoly_state()
+{
+    unsigned char key[32];
+    unsigned char nonce[12];
+    unsigned char aad[1];
+    unsigned char input[1];
+    unsigned char output[1];
+    unsigned char mac[16];
+    size_t input_len = sizeof( input );
+    size_t aad_len = sizeof( aad );
+    mbedtls_chachapoly_context ctx;
+
+    memset( key,    0x00, sizeof( key ) );
+    memset( nonce,  0x00, sizeof( nonce ) );
+    memset( aad,    0x00, sizeof( aad ) );
+    memset( input,  0x00, sizeof( input ) );
+    memset( output, 0x00, sizeof( output ) );
+    memset( mac,    0x00, sizeof( mac ) );
+
+    /* Initial state: finish, update, update_aad forbidden */
+    mbedtls_chachapoly_init( &ctx );
+
+    TEST_ASSERT( mbedtls_chachapoly_finish( &ctx, mac )
+                 == MBEDTLS_ERR_CHACHAPOLY_BAD_STATE );
+    TEST_ASSERT( mbedtls_chachapoly_update( &ctx, input_len, input, output )
+                 == MBEDTLS_ERR_CHACHAPOLY_BAD_STATE );
+    TEST_ASSERT( mbedtls_chachapoly_update_aad( &ctx, aad, aad_len )
+                 == MBEDTLS_ERR_CHACHAPOLY_BAD_STATE );
+
+    /* Still initial state: finish, update, update_aad forbidden */
+    TEST_ASSERT( mbedtls_chachapoly_setkey( &ctx, key )
+                 == 0 );
+
+    TEST_ASSERT( mbedtls_chachapoly_finish( &ctx, mac )
+                 == MBEDTLS_ERR_CHACHAPOLY_BAD_STATE );
+    TEST_ASSERT( mbedtls_chachapoly_update( &ctx, input_len, input, output )
+                 == MBEDTLS_ERR_CHACHAPOLY_BAD_STATE );
+    TEST_ASSERT( mbedtls_chachapoly_update_aad( &ctx, aad, aad_len )
+                 == MBEDTLS_ERR_CHACHAPOLY_BAD_STATE );
+
+    /* Starts -> finish OK */
+    TEST_ASSERT( mbedtls_chachapoly_starts( &ctx, nonce, MBEDTLS_CHACHAPOLY_ENCRYPT )
+                 == 0 );
+    TEST_ASSERT( mbedtls_chachapoly_finish( &ctx, mac )
+                 == 0 );
+
+    /* After finish: update, update_aad forbidden */
+    TEST_ASSERT( mbedtls_chachapoly_update( &ctx, input_len, input, output )
+                 == MBEDTLS_ERR_CHACHAPOLY_BAD_STATE );
+    TEST_ASSERT( mbedtls_chachapoly_update_aad( &ctx, aad, aad_len )
+                 == MBEDTLS_ERR_CHACHAPOLY_BAD_STATE );
+
+    /* Starts -> update* OK */
+    TEST_ASSERT( mbedtls_chachapoly_starts( &ctx, nonce, MBEDTLS_CHACHAPOLY_ENCRYPT )
+                 == 0 );
+    TEST_ASSERT( mbedtls_chachapoly_update( &ctx, input_len, input, output )
+                 == 0 );
+    TEST_ASSERT( mbedtls_chachapoly_update( &ctx, input_len, input, output )
+                 == 0 );
+
+    /* After update: update_aad forbidden */
+    TEST_ASSERT( mbedtls_chachapoly_update_aad( &ctx, aad, aad_len )
+                 == MBEDTLS_ERR_CHACHAPOLY_BAD_STATE );
+
+    /* Starts -> update_aad* -> finish OK */
+    TEST_ASSERT( mbedtls_chachapoly_starts( &ctx, nonce, MBEDTLS_CHACHAPOLY_ENCRYPT )
+                 == 0 );
+    TEST_ASSERT( mbedtls_chachapoly_update_aad( &ctx, aad, aad_len )
+                 == 0 );
+    TEST_ASSERT( mbedtls_chachapoly_update_aad( &ctx, aad, aad_len )
+                 == 0 );
+    TEST_ASSERT( mbedtls_chachapoly_finish( &ctx, mac )
+                 == 0 );
+
+exit:
+    mbedtls_chachapoly_free( &ctx );
+}
+/* END_CASE */
+
 /* BEGIN_CASE depends_on:MBEDTLS_SELF_TEST */
 void chachapoly_selftest()
 {