diff --git a/libguile/gc_os_dep.c b/libguile/gc_os_dep.c
index 7bc96447f..c6241803a 100644
--- a/libguile/gc_os_dep.c
+++ b/libguile/gc_os_dep.c
@@ -1867,11 +1867,14 @@ void *scm_get_stack_base()
     /* Skip the required number of fields.  This number is hopefully	*/
     /* constant across all Linux implementations.			*/
       for (i = 0; i < STAT_SKIP; ++i) {
-	while (isspace(c)) c = stat_buf[buf_offset++];
-	while (!isspace(c)) c = stat_buf[buf_offset++];
+	while (isspace ((int) c)) 
+          c = stat_buf[buf_offset++];
+	while (!isspace ((int) c)) 
+          c = stat_buf[buf_offset++];
       }
-    while (isspace(c)) c = stat_buf[buf_offset++];
-    while (isdigit(c)) {
+      while (isspace ((int) c)) 
+        c = stat_buf[buf_offset++];
+    while (isdigit ((int) c)) {
       result *= 10;
       result += c - '0';
       c = stat_buf[buf_offset++];
diff --git a/libguile/inet_aton.c b/libguile/inet_aton.c
index ebef71f55..c89378bb1 100644
--- a/libguile/inet_aton.c
+++ b/libguile/inet_aton.c
@@ -103,14 +103,14 @@ inet_aton(const char *cp_arg, struct in_addr *addr)
 				base = 8;
 		}
 		while ((c = *cp) != '\0') {
-			if (isascii(c) && isdigit(c)) {
+                        if (isascii ((int) c) && isdigit ((int) c)) {
 				val = (val * base) + (c - '0');
 				cp++;
 				continue;
 			}
-			if (base == 16 && isascii(c) && isxdigit(c)) {
+                        if (base == 16 && isascii ((int) c) && isxdigit ((int) c)) {
 				val = (val << 4) + 
-					(c + 10 - (islower(c) ? 'a' : 'A'));
+                                  (c + 10 - (islower((int) c) ? 'a' : 'A'));
 				cp++;
 				continue;
 			}
@@ -132,7 +132,7 @@ inet_aton(const char *cp_arg, struct in_addr *addr)
 	/*
 	 * Check for trailing characters.
 	 */
-	if (*cp && (!isascii(*cp) || !isspace(*cp)))
+	if (*cp && (!isascii ((int) (*cp)) || !isspace ((int) (*cp))))
 		return (0);
 	/*
 	 * Concoct the address according to
diff --git a/libguile/read.c b/libguile/read.c
index d91c868e1..a784f3421 100644
--- a/libguile/read.c
+++ b/libguile/read.c
@@ -1437,7 +1437,8 @@ scm_scan_for_encoding (SCM port)
   /* grab the next token */
   i = 0;
   while (pos + i - header <= SCM_ENCODING_SEARCH_SIZE 
-	 && (isalnum(pos[i]) || pos[i] == '_' || pos[i] == '-' || pos[i] == '.'))
+	 && (isalnum((int) pos[i]) || pos[i] == '_' || pos[i] == '-' 
+             || pos[i] == '.'))
     i++;
 
   if (i == 0)
diff --git a/libguile/win32-socket.c b/libguile/win32-socket.c
index e845d886a..825b4c499 100644
--- a/libguile/win32-socket.c
+++ b/libguile/win32-socket.c
@@ -435,7 +435,7 @@ scm_i_socket_uncomment (char *line)
       while (end > line && (*end == '\r' || *end == '\n'))
 	*end-- = '\0';
     }
-  while (end > line && isspace (*end))
+  while (end > line && isspace ((int) (*end)))
     *end-- = '\0';
 
   return end;