diff --git a/dlls/cryptui/main.c b/dlls/cryptui/main.c
index 6481c1f08be..c3b0a0ea958 100644
--- a/dlls/cryptui/main.c
+++ b/dlls/cryptui/main.c
@@ -295,7 +295,7 @@ static CERT_ENHKEY_USAGE *convert_usages_str_to_usage(LPSTR usageStr)
         {
             if (comma)
                 *comma = 0;
-            add_oid_to_usage(usage, ptr);
+            usage = add_oid_to_usage(usage, ptr);
         }
     }
     return usage;
@@ -323,7 +323,7 @@ static CERT_ENHKEY_USAGE *create_advanced_filter(void)
                 {
                     PCCRYPT_OID_INFO *ptr;
 
-                    for (ptr = usages; *ptr; ptr++)
+                    for (ptr = usages; advancedUsage && *ptr; ptr++)
                     {
                         DWORD i;
                         BOOL disabled = FALSE;
@@ -334,7 +334,7 @@ static CERT_ENHKEY_USAGE *create_advanced_filter(void)
                              (*ptr)->pszOID))
                                 disabled = TRUE;
                         if (!disabled)
-                            add_oid_to_usage(advancedUsage,
+                            advancedUsage = add_oid_to_usage(advancedUsage,
                              (LPSTR)(*ptr)->pszOID);
                     }
                     /* The individual strings are pointers to disabledUsagesStr,