diff --git a/mongoose.c b/mongoose.c
index 41982a9a..de69c569 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -2230,7 +2230,7 @@ struct mg_fs mg_fs_posix = {p_stat,  p_list, p_open,   p_close,  p_read,
 static int mg_ncasecmp(const char *s1, const char *s2, size_t len) {
   int diff = 0;
   if (len > 0) do {
-      char c = *s1++, d = *s2++;
+      int c = *s1++, d = *s2++;
       if (c >= 'A' && c <= 'Z') c += 'a' - 'A';
       if (d >= 'A' && d <= 'Z') d += 'a' - 'A';
       diff = c - d;
@@ -8033,14 +8033,14 @@ struct mg_str mg_str_n(const char *s, size_t n) {
   return str;
 }
 
-static char tolc(char c) {
+static int mg_tolc(char c) {
   return (c >= 'A' && c <= 'Z') ? c + 'a' - 'A' : c;
 }
 
 int mg_casecmp(const char *s1, const char *s2) {
   int diff = 0;
   do {
-    char c = tolc(*s1++), d = tolc(*s2++);
+    int c = mg_tolc(*s1++), d = mg_tolc(*s2++);
     diff = c - d;
   } while (diff == 0 && s1[-1] != '\0');
   return diff;
@@ -8049,8 +8049,8 @@ int mg_casecmp(const char *s1, const char *s2) {
 int mg_strcmp(const struct mg_str str1, const struct mg_str str2) {
   size_t i = 0;
   while (i < str1.len && i < str2.len) {
-    char c1 = str1.buf[i];
-    char c2 = str2.buf[i];
+    int c1 = str1.buf[i];
+    int c2 = str2.buf[i];
     if (c1 < c2) return -1;
     if (c1 > c2) return 1;
     i++;
@@ -8063,8 +8063,8 @@ int mg_strcmp(const struct mg_str str1, const struct mg_str str2) {
 int mg_strcasecmp(const struct mg_str str1, const struct mg_str str2) {
   size_t i = 0;
   while (i < str1.len && i < str2.len) {
-    char c1 = tolc(str1.buf[i]);
-    char c2 = tolc(str2.buf[i]);
+    int c1 = mg_tolc(str1.buf[i]);
+    int c2 = mg_tolc(str2.buf[i]);
     if (c1 < c2) return -1;
     if (c1 > c2) return 1;
     i++;
diff --git a/src/http.c b/src/http.c
index e4bd1131..3f33b880 100644
--- a/src/http.c
+++ b/src/http.c
@@ -14,7 +14,7 @@
 static int mg_ncasecmp(const char *s1, const char *s2, size_t len) {
   int diff = 0;
   if (len > 0) do {
-      char c = *s1++, d = *s2++;
+      int c = *s1++, d = *s2++;
       if (c >= 'A' && c <= 'Z') c += 'a' - 'A';
       if (d >= 'A' && d <= 'Z') d += 'a' - 'A';
       diff = c - d;
diff --git a/src/str.c b/src/str.c
index 4b0fa9a8..dc8fed3e 100644
--- a/src/str.c
+++ b/src/str.c
@@ -10,14 +10,14 @@ struct mg_str mg_str_n(const char *s, size_t n) {
   return str;
 }
 
-static char tolc(char c) {
+static int mg_tolc(char c) {
   return (c >= 'A' && c <= 'Z') ? c + 'a' - 'A' : c;
 }
 
 int mg_casecmp(const char *s1, const char *s2) {
   int diff = 0;
   do {
-    char c = tolc(*s1++), d = tolc(*s2++);
+    int c = mg_tolc(*s1++), d = mg_tolc(*s2++);
     diff = c - d;
   } while (diff == 0 && s1[-1] != '\0');
   return diff;
@@ -26,8 +26,8 @@ int mg_casecmp(const char *s1, const char *s2) {
 int mg_strcmp(const struct mg_str str1, const struct mg_str str2) {
   size_t i = 0;
   while (i < str1.len && i < str2.len) {
-    char c1 = str1.buf[i];
-    char c2 = str2.buf[i];
+    int c1 = str1.buf[i];
+    int c2 = str2.buf[i];
     if (c1 < c2) return -1;
     if (c1 > c2) return 1;
     i++;
@@ -40,8 +40,8 @@ int mg_strcmp(const struct mg_str str1, const struct mg_str str2) {
 int mg_strcasecmp(const struct mg_str str1, const struct mg_str str2) {
   size_t i = 0;
   while (i < str1.len && i < str2.len) {
-    char c1 = tolc(str1.buf[i]);
-    char c2 = tolc(str2.buf[i]);
+    int c1 = mg_tolc(str1.buf[i]);
+    int c2 = mg_tolc(str2.buf[i]);
     if (c1 < c2) return -1;
     if (c1 > c2) return 1;
     i++;