diff --git a/libretro-common/streams/file_stream.c b/libretro-common/streams/file_stream.c
index 4caee7b932..280eaf59ad 100644
--- a/libretro-common/streams/file_stream.c
+++ b/libretro-common/streams/file_stream.c
@@ -255,7 +255,7 @@ int filestream_scanf(RFILE *stream, const char* format, ...)
             *subfmtiter++ = *format++;
          }
 
-         while (isdigit(*format))
+         while (isdigit((unsigned char)*format))
             *subfmtiter++ = *format++; /* width */
 
          /* length */
@@ -311,9 +311,9 @@ int filestream_scanf(RFILE *stream, const char* format, ...)
          ret++;
          bufiter += sublen;
       }
-      else if (isspace(*format))
+      else if (isspace((unsigned char)*format))
       {
-         while (isspace(*bufiter))
+         while (isspace((unsigned char)*bufiter))
             bufiter++;
          format++;
       }
diff --git a/libretro-common/string/stdstring.c b/libretro-common/string/stdstring.c
index ab8ade2c74..fd01239bed 100644
--- a/libretro-common/string/stdstring.c
+++ b/libretro-common/string/stdstring.c
@@ -355,7 +355,7 @@ unsigned string_to_unsigned(const char *str)
 
    for (ptr = str; *ptr != '\0'; ptr++)
    {
-      if (!isdigit(*ptr))
+      if (!isdigit((unsigned char)*ptr))
          return 0;
    }
 
@@ -388,7 +388,7 @@ unsigned string_hex_to_unsigned(const char *str)
    /* Check for valid characters */
    for (ptr = hex_str; *ptr != '\0'; ptr++)
    {
-      if (!isxdigit(*ptr))
+      if (!isxdigit((unsigned char)*ptr))
          return 0;
    }