diff --git a/src/HttpServer.c b/src/HttpServer.c
index b1ee986..a81e638 100644
--- a/src/HttpServer.c
+++ b/src/HttpServer.c
@@ -507,14 +507,14 @@ HttpServerWorkerThread(void *args)
 
             headerPtr = line + i + 1;
 
-            while (isspace(*headerPtr))
+            while (isspace((unsigned char) *headerPtr))
             {
                 headerPtr++;
             }
 
             for (i = lineLen - 1; i > (line + lineLen) - headerPtr; i--)
             {
-                if (!isspace(line[i]))
+                if (!isspace((unsigned char) line[i]))
                 {
                     break;
                 }
diff --git a/src/Log.c b/src/Log.c
index 33b7600..f7c6107 100644
--- a/src/Log.c
+++ b/src/Log.c
@@ -294,7 +294,7 @@ Log(LogConfig * config, int level, const char *msg,...)
         if (tsLength)
         {
             fputs(tsBuffer, config->out);
-            if (!isspace(tsBuffer[tsLength - 1]))
+            if (!isspace((unsigned char) tsBuffer[tsLength - 1]))
             {
                 fputc(' ', config->out);
             }
diff --git a/src/TelodendriaConfig.c b/src/TelodendriaConfig.c
index 0c846f1..dff1a1c 100644
--- a/src/TelodendriaConfig.c
+++ b/src/TelodendriaConfig.c
@@ -38,7 +38,7 @@ IsInteger(char *str)
 {
     while (*str)
     {
-        if (!isdigit(*str))
+        if (!isdigit((unsigned char) *str))
         {
             return 0;
         }