diff --git a/libraries/AP_Common/AP_Common.h b/libraries/AP_Common/AP_Common.h
index 71c2f112e1..2aa11ec7f6 100644
--- a/libraries/AP_Common/AP_Common.h
+++ b/libraries/AP_Common/AP_Common.h
@@ -105,9 +105,34 @@ static inline int strcmp_P(const char *str1, const prog_char_t *pstr)
     return strcmp_P(str1, (const prog_char *)pstr);
 }
 
-static inline size_t strlcat_P(char *buffer, const prog_char_t *pstr, size_t buffer_size)
+static inline size_t strlen_P(const prog_char_t *pstr)
 {
-    return strlcat_P(buffer, (const prog_char *)pstr, buffer_size);
+    return strlen_P((const prog_char *)pstr);
+}
+
+// strlcat_P() in AVR libc seems to be broken 
+static inline size_t strlcat_P(char *d, const prog_char_t *s, size_t bufsize)
+{
+	size_t len1 = strlen(d);
+	size_t len2 = strlen_P(s);
+	size_t ret = len1 + len2;
+    
+	if (len1+len2 >= bufsize) {
+		if (bufsize < (len1+1)) {
+			return ret;
+		}
+		len2 = bufsize - (len1+1);
+	}
+	if (len2 > 0) {
+		memcpy_P(d+len1, s, len2);
+		d[len1+len2] = 0;
+	}
+	return ret;
+}
+
+static inline char *strncpy_P(char *buffer, const prog_char_t *pstr, size_t buffer_size)
+{
+    return strncpy_P(buffer, (const prog_char *)pstr, buffer_size);
 }