diff --git a/library/pkcs5.c b/library/pkcs5.c
index 79d67e9..280453a 100644
--- a/library/pkcs5.c
+++ b/library/pkcs5.c
@@ -97,7 +97,7 @@
     if( ( ret = asn1_get_alg_null( &p, end, &prf_alg_oid ) ) != 0 )
         return( POLARSSL_ERR_PKCS5_INVALID_FORMAT + ret );
 
-    if( !OID_CMP( OID_HMAC_SHA1, &prf_alg_oid ) )
+    if( OID_CMP( OID_HMAC_SHA1, &prf_alg_oid ) != 0 )
         return( POLARSSL_ERR_PKCS5_FEATURE_UNAVAILABLE );
 
     *md_type = POLARSSL_MD_SHA1;
@@ -145,7 +145,7 @@
 
     // Only PBKDF2 supported at the moment
     //
-    if( !OID_CMP( OID_PKCS5_PBKDF2, &kdf_alg_oid ) )
+    if( OID_CMP( OID_PKCS5_PBKDF2, &kdf_alg_oid ) != 0 )
         return( POLARSSL_ERR_PKCS5_FEATURE_UNAVAILABLE );
 
     if( ( ret = pkcs5_parse_pbkdf2_params( &kdf_alg_params,
diff --git a/library/pkparse.c b/library/pkparse.c
index 1529a93..b42bf8b 100644
--- a/library/pkparse.c
+++ b/library/pkparse.c
@@ -997,7 +997,7 @@
 
         decrypted = 1;
     }
-    else if( OID_CMP( OID_PKCS12_PBE_SHA1_RC4_128, &pbe_alg_oid ) )
+    else if( OID_CMP( OID_PKCS12_PBE_SHA1_RC4_128, &pbe_alg_oid ) == 0 )
     {
         if( ( ret = pkcs12_pbe_sha1_rc4_128( &pbe_params,
                                              PKCS12_PBE_DECRYPT,
@@ -1018,7 +1018,7 @@
     else
 #endif /* POLARSSL_PKCS12_C */
 #if defined(POLARSSL_PKCS5_C)
-    if( OID_CMP( OID_PKCS5_PBES2, &pbe_alg_oid ) )
+    if( OID_CMP( OID_PKCS5_PBES2, &pbe_alg_oid ) == 0 )
     {
         if( ( ret = pkcs5_pbes2( &pbe_params, PKCS5_DECRYPT, pwd, pwdlen,
                                   p, len, buf ) ) != 0 )
diff --git a/library/x509.c b/library/x509.c
index c1fd8ad..33b1ac3 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -269,7 +269,7 @@
             return( ret );
 
         /* Only MFG1 is recognised for now */
-        if( ! OID_CMP( OID_MGF1, &alg_id ) )
+        if( OID_CMP( OID_MGF1, &alg_id ) != 0 )
             return( POLARSSL_ERR_X509_FEATURE_UNAVAILABLE +
                     POLARSSL_ERR_OID_NOT_FOUND );
 
diff --git a/library/x509_crt.c b/library/x509_crt.c
index 84e4415..8b93473 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -1417,7 +1417,7 @@
             return( 0 );
         }
 
-        if( OID_CMP( OID_ANY_EXTENDED_KEY_USAGE, cur_oid ) )
+        if( OID_CMP( OID_ANY_EXTENDED_KEY_USAGE, cur_oid ) == 0 )
             return( 0 );
     }
 
@@ -1961,7 +1961,7 @@
         {
             while( name != NULL )
             {
-                if( OID_CMP( OID_AT_CN, &name->oid ) )
+                if( OID_CMP( OID_AT_CN, &name->oid ) == 0 )
                 {
                     if( name->val.len == cn_len &&
                         x509_memcasecmp( name->val.p, cn, cn_len ) == 0 )