diff --git a/src/cheatman.c b/src/cheatman.c
index e992713ef..26858865a 100644
--- a/src/cheatman.c
+++ b/src/cheatman.c
@@ -75,7 +75,7 @@ static code_t make_code(const char *s)
     int i = 0;
 
     while (*s) {
-        if (isxdigit(*s))
+        if (isxdigit((int)*s))
             digits[i++] = *s;
         s++;
     }
@@ -99,10 +99,10 @@ static int is_cheat_code(const char *s)
     int i = 0;
 
     while (*s) {
-        if (isxdigit(*s)) {
+        if (isxdigit((int)*s)) {
             if (++i > CODE_DIGITS)
                 return 0;
-        } else if (!isspace(*s)) {
+        } else if (!isspace((int)*s)) {
             return 0;
         }
         s++;
@@ -178,7 +178,7 @@ static int is_empty_str(const char *s)
     size_t slen = strlen(s);
 
     while (slen--) {
-        if (isgraph(*s++))
+        if (isgraph((int)*s++))
             return 0;
     }
 
@@ -200,13 +200,13 @@ static int trim_str(char *s)
         return -1;
 
     /* Get first non-space char */
-    while (isspace(*t++))
+    while (isspace((int)*t++))
         first++;
 
     /* Get last non-space char */
     last = strlen(s) - 1;
     t = &s[last];
-    while (isspace(*t--))
+    while (isspace((int)*t--))
         last--;
 
     /* Kill leading/trailing spaces */
@@ -224,7 +224,7 @@ static int trim_str(char *s)
 static int is_empty_substr(const char *s, size_t count)
 {
     while (count--) {
-        if (isgraph(*s++))
+        if (isgraph((int)*s++))
             return 0;
     }
 
diff --git a/src/opl.c b/src/opl.c
index 2074a2e5a..61de8d714 100644
--- a/src/opl.c
+++ b/src/opl.c
@@ -401,7 +401,7 @@ int oplPath2Mode(const char *path)
             if (blkdevnameend != NULL) {
                 blkdevnamelen = (int)(blkdevnameend - appsPath);
 
-                while ((blkdevnamelen > 0) && isdigit(appsPath[blkdevnamelen - 1]))
+                while ((blkdevnamelen > 0) && isdigit((int)appsPath[blkdevnamelen - 1]))
                     blkdevnamelen--; //Ignore the unit number.
 
                 if (strncmp(path, appsPath, blkdevnamelen) == 0)
diff --git a/src/ps2cnf.c b/src/ps2cnf.c
index 6beb72f22..bb2f97994 100644
--- a/src/ps2cnf.c
+++ b/src/ps2cnf.c
@@ -15,7 +15,7 @@
 
 static const char *CNFGetToken(const char *cnf, const char *key)
 {
-    for (; isspace(*cnf); cnf++) {
+    for (; isspace((int)*cnf); cnf++) {
     }
 
     for (; *key != '\0'; key++, cnf++) {
@@ -45,7 +45,7 @@ static const char *CNFGetKey(const char *line, char *key)
     int i;
 
     //Skip leading whitespace
-    for (; isspace(*line); line++) {
+    for (; isspace((int)*line); line++) {
     }
 
     if (*line == '\0') { //Unexpected end of file
@@ -53,11 +53,11 @@ static const char *CNFGetKey(const char *line, char *key)
     }
 
     for (i = 0; i < CNF_PATH_LEN_MAX && *line != '\0'; i++) {
-        if (isgraph(*line)) {
+        if (isgraph((int)*line)) {
             *key = *line;
             line++;
             key++;
-        } else if (isspace(*line)) {
+        } else if (isspace((int)*line)) {
             *key = '\0';
             break;
         } else if (*line == '\0') { //Unexpected end of file. This check exists, along with the other similar check above.