diff --git a/mhl/env.h b/mhl/env.h
index 8d5633797..6598e0cbf 100644
--- a/mhl/env.h
+++ b/mhl/env.h
@@ -1,5 +1,5 @@
-#ifndef __MHL_ENV_H
-#define __MHL_ENV_H
+#ifndef MHL_ENV_H
+#define MHL_ENV_H
 
 #include <mhl/string.h>
 
diff --git a/mhl/escape.h b/mhl/escape.h
index 2ec4e0d46..118e08269 100644
--- a/mhl/escape.h
+++ b/mhl/escape.h
@@ -1,5 +1,5 @@
-#ifndef __MHL_SHELL_ESCAPE_H
-#define __MHL_SHELL_ESCAPE_H
+#ifndef MHL_ESCAPE_H
+#define MHL_ESCAPE_H
 
 /* Micro helper library: shell escaping functions */
 
@@ -64,7 +64,7 @@ static inline SHELL_ESCAPED_STR mhl_shell_escape_dup(const char* src)
 /** Unescape paths or other strings for e.g the internal cd
     shell-unescape within a given buffer (writing to it!)
 
- /params const char * in
+ /params const char * src
  string for unescaping
  /returns
  return unescaped string
@@ -113,7 +113,7 @@ static inline char* mhl_shell_unescape_buf(char* text)
 		case '`':
 		case '"':
 		case ';':
-		case '\0': /* end of line! malformed escape string */
+		case '\0': /* end of string! malformed escape string */
 		    goto out;
 		default:
 		    (*writeptr) = c; writeptr++; break;
diff --git a/mhl/memory.h b/mhl/memory.h
index b00617700..3268e93a1 100644
--- a/mhl/memory.h
+++ b/mhl/memory.h
@@ -1,5 +1,5 @@
-#ifndef __MHL_MEM
-#define __MHL_MEM
+#ifndef MHL_MEMORY_H
+#define MHL_MEMORY_H
 
 #include <memory.h>
 #include <stdlib.h>
@@ -17,7 +17,7 @@ static inline void mhl_mem_free(void* ptr)
 }
 
 /* free an ptr and NULL it */
-#define 	MHL_PTR_FREE(ptr)	do { mhl_mem_free(ptr); (ptr) = NULL; } while (0); 
+#define 	MHL_PTR_FREE(ptr)	do { mhl_mem_free(ptr); (ptr) = NULL; } while (0)
 
 /* allocate a chunk on stack - automatically free'd on function exit */
 #define		mhl_stack_alloc(sz)	(alloca(sz))
diff --git a/mhl/strhash.h b/mhl/strhash.h
index 1f195053c..8ff17cba6 100644
--- a/mhl/strhash.h
+++ b/mhl/strhash.h
@@ -1,5 +1,5 @@
-#ifndef __MHL_STRHASH_H
-#define __MHL_STRHASH_H
+#ifndef MHL_STRHASH_H
+#define MHL_STRHASH_H
 
 #include <hash.h>
 #include <mhl/memory.h>
diff --git a/mhl/string.h b/mhl/string.h
index 47f097f1e..3b4c421f1 100644
--- a/mhl/string.h
+++ b/mhl/string.h
@@ -1,5 +1,5 @@
-#ifndef __MHL_STRING_H
-#define __MHL_STRING_H
+#ifndef MHL_STRING_H
+#define MHL_STRING_H
 
 #include <ctype.h>
 #include <stdarg.h>
@@ -10,6 +10,9 @@
 #define mhl_str_ndup(str,len)	((str ? strndup(str,len) : strdup("")))
 #define mhl_str_len(str)	((str ? strlen(str) : 0))
 
+#define ISSPACE(c)		isspace((unsigned char)(c))
+#define TOUPPER(c)		toupper((unsigned char)(c))
+
 static inline char * mhl_str_dup_range(const char * s_start, const char * s_bound)
 {
     return mhl_str_ndup(s_start, s_bound - s_start);
@@ -20,26 +23,26 @@ static inline char* mhl_str_trim(char* str)
     if (!str) return NULL;	/* NULL string ?! bail out. */
 
     /* find the first non-space */
-    char* start; for (start=str; ((*str) && (!isspace(*str))); str++);
+    char* start; for (start=str; ((*str) && (!ISSPACE(*str))); str++);
 
     /* only spaces ? */
     if (!(*str)) { *str = 0; return str; }
 
-    /* get the size (cannot be empty - catched above) */
+    /* get the size (cannot be empty - caught above) */
     size_t _sz = strlen(str);
 
     /* find the proper end */
     char* end;
-    for (end=(str+_sz-1); ((end>str) && (isspace(*end))); end--);
+    for (end=(str+_sz-1); ((end>str) && (ISSPACE(*end))); end--);
     end[1] = 0;		/* terminate, just to be sure */
 
     /* if we have no leading spaces, just trucate */
     if (start==str) { end++; *end = 0; return str; }
 
-    /* if it' only one char, dont need memmove for that */
+    /* if it's only one char, dont need memmove for that */
     if (start==end) { str[0]=*start; str[1]=0; return str; }
 
-    /* by here we have a (non-empty) region between start end end */
+    /* by here we have a (non-empty) region between start and end */
     memmove(str,start,(end-start+1));
     return str;
 }
@@ -48,7 +51,7 @@ static inline void mhl_str_toupper(char* str)
 {
     if (str)
 	for (;*str;str++)
-	    *str = toupper(*str);
+	    *str = TOUPPER(*str);
 }
 
 /* note: we use ((char*)(1)) as terminator - NULL is a valid argument ! */
@@ -127,6 +130,7 @@ static inline char * mhl_strmove(char * dest, const char * src)
 {
     size_t n = strlen (src) + 1; /* + '\0' */
 
+    /* strictly speaking, this invokes undefined behavior as soon as dest and src are pointers into different objects. */
     assert (dest<=src);
 
     return memmove(dest, src, n);
@@ -165,4 +169,4 @@ static inline char* mhl_str_dir_plus_file(const char* dirname, const char* filen
     return buffer;
 }
 
-#endif /* __MHL_STRING_H */
+#endif /* MHL_STRING_H */
diff --git a/mhl/types.h b/mhl/types.h
index 1f8400299..977c27a2c 100644
--- a/mhl/types.h
+++ b/mhl/types.h
@@ -4,13 +4,15 @@
 
 */
 
-#ifndef __MHL_TYPES_H
-#define __MHL_TYPES_H
+#ifndef MHL_TYPES_H
+#define MHL_TYPES_H
 
-typedef enum 
+#if !defined(__bool_true_false_are_defined) && !defined(false) && !defined(true) && !defined(bool)
+typedef enum
 {
     false	= 0,
     true	= 1
 } bool;
+#endif
 
 #endif