diff --git a/include/mbedtls/pk.h b/include/mbedtls/pk.h
index f7fa4d31a..36fdea5be 100644
--- a/include/mbedtls/pk.h
+++ b/include/mbedtls/pk.h
@@ -475,7 +475,7 @@ int mbedtls_pk_sign( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
  *
  * \return          Maximum size in bytes of a signature made with this key.
  */
-size_t mbedtls_pk_signature_size( const mbedtls_pk_context *ctx );
+size_t mbedtls_pk_get_signature_size( const mbedtls_pk_context *ctx );
 
 /**
  * \brief           Decrypt message (including padding if relevant).
diff --git a/include/mbedtls/pk_info.h b/include/mbedtls/pk_info.h
index d1d95ef4f..a8b735fd1 100644
--- a/include/mbedtls/pk_info.h
+++ b/include/mbedtls/pk_info.h
@@ -120,9 +120,11 @@ struct mbedtls_pk_info_t
      * usage restrictions into account. */
     int (*can_do)( const void * ctx, mbedtls_pk_type_t type );
 
-    /** Signature size
+    /** Upper bound of the signature length
      *
-     * mbedtls_pk_signature_size() returns this value.
+     * mbedtls_pk_get_signature_size() returns this value.
+     *
+     * In case of an error, or an unsupported key type, 0 should be returned.
      *
      * Opaque implementations may omit this method if they do not support
      * signature. */
diff --git a/library/pk.c b/library/pk.c
index 52bcb8669..4213001e8 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -357,7 +357,7 @@ size_t mbedtls_pk_get_bitlen( const mbedtls_pk_context *ctx )
 /*
  * Maximum signature size
  */
-size_t mbedtls_pk_signature_size( const mbedtls_pk_context *ctx )
+size_t mbedtls_pk_get_signature_size( const mbedtls_pk_context *ctx )
 {
     if( ctx == NULL || ctx->pk_info == NULL )
         return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );
diff --git a/tests/suites/test_suite_pk.function b/tests/suites/test_suite_pk.function
index bd92f0c99..e660e1192 100644
--- a/tests/suites/test_suite_pk.function
+++ b/tests/suites/test_suite_pk.function
@@ -100,7 +100,7 @@ static void pk_rsa_match( mbedtls_rsa_context *raw,
     TEST_ASSERT( mbedtls_pk_can_do( tested_ctx, MBEDTLS_PK_RSA ) );
     TEST_ASSERT( mbedtls_pk_get_bitlen( tested_ctx ) == RSA_KEY_SIZE );
     TEST_ASSERT( mbedtls_pk_get_len( tested_ctx ) == RSA_KEY_LEN );
-    TEST_ASSERT( mbedtls_pk_signature_size( tested_ctx ) == RSA_KEY_LEN );
+    TEST_ASSERT( mbedtls_pk_get_signature_size( tested_ctx ) == RSA_KEY_LEN );
 
     /* Test signature */
     TEST_ASSERT( mbedtls_pk_sign( tested_ctx, MBEDTLS_MD_NONE, hash, sizeof hash,
@@ -533,7 +533,7 @@ void pk_sign_verify( int type, int sign_ret, int verify_ret )
     TEST_ASSERT( mbedtls_pk_sign( &pk, MBEDTLS_MD_SHA256, hash, sizeof hash,
                           sig, &sig_len, rnd_std_rand, NULL ) == sign_ret );
     if( sign_ret == 0 )
-        TEST_ASSERT( sig_len <= mbedtls_pk_signature_size( &pk ) );
+        TEST_ASSERT( sig_len <= mbedtls_pk_get_signature_size( &pk ) );
 
     TEST_ASSERT( mbedtls_pk_verify( &pk, MBEDTLS_MD_SHA256,
                             hash, sizeof hash, sig, sig_len ) == verify_ret );
@@ -774,7 +774,7 @@ void pk_opaque_mock( )
     TEST_ASSERT( mbedtls_pk_get_bitlen( &ctx ) == OPAQUE_MOCK_BITLEN );
     TEST_ASSERT( mbedtls_pk_can_do( &ctx, OPAQUE_MOCK_CAN_DO ) == 1 );
     TEST_ASSERT( mbedtls_pk_can_do( &ctx, OPAQUE_MOCK_CAN_DO ^ 1 ) == 0 );
-    TEST_ASSERT( mbedtls_pk_signature_size( &ctx ) == OPAQUE_MOCK_SIGNATURE_SIZE );
+    TEST_ASSERT( mbedtls_pk_get_signature_size( &ctx ) == OPAQUE_MOCK_SIGNATURE_SIZE );
 
     TEST_ASSERT( mbedtls_pk_verify( &ctx, OPAQUE_MOCK_MD_ALG,
                                     opaque_mock_hash, sizeof( opaque_mock_hash ),
@@ -881,7 +881,7 @@ void pk_opaque_minimal( )
     TEST_ASSERT( mbedtls_pk_get_bitlen( &ctx ) == OPAQUE_MOCK_BITLEN );
     TEST_ASSERT( mbedtls_pk_can_do( &ctx, OPAQUE_MOCK_CAN_DO ) == 1 );
     TEST_ASSERT( mbedtls_pk_can_do( &ctx, OPAQUE_MOCK_CAN_DO ^ 1 ) == 0 );
-    TEST_ASSERT( mbedtls_pk_signature_size( &ctx ) == 0 );
+    TEST_ASSERT( mbedtls_pk_get_signature_size( &ctx ) == 0 );
 
     TEST_ASSERT( mbedtls_pk_verify( &ctx, OPAQUE_MOCK_MD_ALG,
                                     NULL, 0, NULL, 0 ) ==