diff --git a/libs/libc/stdlib/lib_strtoul.c b/libs/libc/stdlib/lib_strtoul.c
index 3f4959aab79..cc7025afd6d 100644
--- a/libs/libc/stdlib/lib_strtoul.c
+++ b/libs/libc/stdlib/lib_strtoul.c
@@ -52,9 +52,10 @@
 
 unsigned long strtoul(FAR const char *nptr, FAR char **endptr, int base)
 {
+  FAR const char *origin = nptr;
   unsigned long accum = 0;
   unsigned long limit;
-  int value;
+  int value = -1;
   int last_digit;
   char sign = 0;
 
@@ -79,7 +80,6 @@ unsigned long strtoul(FAR const char *nptr, FAR char **endptr, int base)
       if (base < 0)
         {
           set_errno(EINVAL);
-          accum = 0;
         }
       else
         {
@@ -127,7 +127,7 @@ unsigned long strtoul(FAR const char *nptr, FAR char **endptr, int base)
             }
         }
 
-      *endptr = (FAR char *)nptr;
+      *endptr = (FAR char *)(value == -1 ? origin : nptr);
     }
 
   return accum;
diff --git a/libs/libc/string/lib_isbasedigit.c b/libs/libc/string/lib_isbasedigit.c
index 2a2d6dd3c63..c9d5b772ae4 100644
--- a/libs/libc/string/lib_isbasedigit.c
+++ b/libs/libc/string/lib_isbasedigit.c
@@ -80,7 +80,7 @@ bool lib_isbasedigit(int ch, int base, int *value)
         }
     }
 
-  if (value)
+  if (ret && value)
     {
       *value = tmp;
     }