diff --git a/src/ngircd/irc-login.c b/src/ngircd/irc-login.c
index 5ec6162c..80a6627f 100644
--- a/src/ngircd/irc-login.c
+++ b/src/ngircd/irc-login.c
@@ -443,7 +443,7 @@ IRC_USER(CLIENT * Client, REQUEST * Req)
 		   punctuation is allowed.*/
 		ptr = Req->argv[0];
 		while (*ptr) {
-			if (!isalnum(*ptr) &&
+			if (!isalnum((int)*ptr) &&
 			    *ptr != '+' && *ptr != '-' &&
 			    *ptr != '.' && *ptr != '_') {
 				Conn_Close(Client_Conn(Client), NULL,
diff --git a/src/tool/tool.c b/src/tool/tool.c
index eb6c131e..1bb3ebe6 100644
--- a/src/tool/tool.c
+++ b/src/tool/tool.c
@@ -84,7 +84,7 @@ ngt_UpperStr(char *String)
 
 	ptr = String;
 	while(*ptr) {
-		*ptr = toupper(*ptr);
+		*ptr = toupper((int)*ptr);
 		ptr++;
 	}
 	return String;
@@ -103,7 +103,7 @@ ngt_LowerStr(char *String)
 
 	ptr = String;
 	while(*ptr) {
-		*ptr = tolower(*ptr);
+		*ptr = tolower((int)*ptr);
 		ptr++;
 	}
 	return String;