diff --git a/api/String.cpp b/api/String.cpp
index 5bf5862a..b67e99c8 100644
--- a/api/String.cpp
+++ b/api/String.cpp
@@ -45,6 +45,12 @@ String::String(const char *cstr)
 	if (cstr) copy(cstr, strlen(cstr));
 }
 
+String::String(const char *cstr, unsigned int length)
+{
+	init();
+	if (cstr) copy(cstr, length);
+}
+
 String::String(const String &value)
 {
 	init();
@@ -626,10 +632,7 @@ String String::substring(unsigned int left, unsigned int right) const
 	String out;
 	if (left >= len) return out;
 	if (right > len) right = len;
-	char temp = buffer[right];  // save the replaced character
-	buffer[right] = '\0';	
-	out = buffer + left;  // pointer arithmetic
-	buffer[right] = temp;  //restore character
+	out.copy(buffer + left, right - left);
 	return out;
 }
 
diff --git a/api/String.h b/api/String.h
index d8f943eb..a3d0d9e8 100644
--- a/api/String.h
+++ b/api/String.h
@@ -68,6 +68,8 @@ class String
 	// fails, the string will be marked as invalid (i.e. "if (s)" will
 	// be false).
 	String(const char *cstr = "");
+	String(const char *cstr, unsigned int length);
+	String(const uint8_t *cstr, unsigned int length) : String((const char*)cstr, length) {}
 	String(const String &str);
 	String(const __FlashStringHelper *str);
 	#if __cplusplus >= 201103L || defined(__GXX_EXPERIMENTAL_CXX0X__)
@@ -109,6 +111,8 @@ class String
 	// concatenation is considered unsucessful.
 	unsigned char concat(const String &str);
 	unsigned char concat(const char *cstr);
+	unsigned char concat(const char *cstr, unsigned int length);
+	unsigned char concat(const uint8_t *cstr, unsigned int length) {return concat((const char*)cstr, length);}
 	unsigned char concat(char c);
 	unsigned char concat(unsigned char num);
 	unsigned char concat(int num);
@@ -225,7 +229,6 @@ class String
 	void init(void);
 	void invalidate(void);
 	unsigned char changeBuffer(unsigned int maxStrLen);
-	unsigned char concat(const char *cstr, unsigned int length);
 
 	// copy and move
 	String & copy(const char *cstr, unsigned int length);