diff --git a/apps/shell/shell-base64.c b/apps/shell/shell-base64.c
index ca723748c..30d921d34 100644
--- a/apps/shell/shell-base64.c
+++ b/apps/shell/shell-base64.c
@@ -86,7 +86,7 @@ base64_decode_char(char c)
 static int
 base64_add_char(struct base64_decoder_state *s, char c)
 {
-  if(isspace(c)) {
+  if(isspace((int)c)) {
     return 0;
   }
 
diff --git a/apps/shell/shell.c b/apps/shell/shell.c
index 62bf7a4d7..b02f45c31 100644
--- a/apps/shell/shell.c
+++ b/apps/shell/shell.c
@@ -532,7 +532,7 @@ shell_strtolong(const char *str, const char **retstr)
     ++strptr;
   }
   
-  for(i = 0; i < 10 && isdigit(strptr[i]); ++i) {
+  for(i = 0; i < 10 && isdigit((int)strptr[i]); ++i) {
     num = num * 10 + strptr[i] - '0';
   }
   if(retstr != NULL) {