--- a/src/core/ngx_string.h
+++ b/src/core/ngx_string.h
@@ -7,12 +7,12 @@
 
 
 typedef struct {
-    size_t  len;
-    char   *data;
+    size_t    len;
+    u_char   *data;
 } ngx_str_t;
 
 
-#define ngx_string(str)  { sizeof(str) - 1, str }
+#define ngx_string(str)  { sizeof(str) - 1, (u_char *) str }
 #define ngx_null_string  { 0, NULL }
 
 
@@ -26,8 +26,10 @@ typedef struct {
 
 #else
 
-#define ngx_strncasecmp           strncasecmp
-#define ngx_strcasecmp            strcasecmp
+#define ngx_strncasecmp(s1, s2, n)                                           \
+                          strncasecmp((const char *) s1, (const char *) s2, n)
+#define ngx_strcasecmp(s1, s2)                                               \
+                          strcasecmp((const char *) s1, (const char *) s2)
 
 #define ngx_snprintf              snprintf
 #define ngx_vsnprintf             vsnprintf
@@ -35,13 +37,14 @@ typedef struct {
 #endif
 
 
-#define ngx_strncmp               strncmp
+#define ngx_strncmp(s1, s2, n)                                               \
+                          strncmp((const char *) s1, (const char *) s2, n)
 
 /* msvc and icc compile strcmp() to inline loop */
-#define ngx_strcmp                strcmp
+#define ngx_strcmp(s1, s2)        strcmp((const char *) s1, (const char *) s2)
 
-#define ngx_strstr                strstr
-#define ngx_strlen                strlen
+#define ngx_strstr(s1, s2)        strstr((const char *) s1, (const char *) s2)
+#define ngx_strlen(s)             strlen((const char *) s)
 
 /*
  * msvc and icc compile memset() to inline "rep stos"
@@ -53,16 +56,16 @@ typedef struct {
 
 /* msvc and icc compile memcpy() to inline "rep movs" */
 #define ngx_memcpy(dst, src, n)   memcpy(dst, src, n)
-#define ngx_cpymem(dst, src, n)   ((char *) memcpy(dst, src, n)) + n
+#define ngx_cpymem(dst, src, n)   ((u_char *) memcpy(dst, src, n)) + n
 
 /* msvc and icc compile memcmp() to inline loop */
 #define ngx_memcmp                memcmp
 
-char *ngx_cpystrn(char *dst, char *src, size_t n);
-int ngx_rstrncmp(char *s1, char *s2, size_t n);
-int ngx_atoi(char *line, size_t n);
+u_char *ngx_cpystrn(u_char *dst, u_char *src, size_t n);
+ngx_int_t ngx_rstrncmp(u_char *s1, u_char *s2, size_t n);
+ngx_int_t ngx_atoi(u_char *line, size_t n);
 
-void ngx_md5_text(char *text, u_char *md5);
+void ngx_md5_text(u_char *text, u_char *md5);
 
 
 #define  ngx_qsort                qsort