diff --git a/cores/arduino/HardwareSerial.cpp b/cores/arduino/HardwareSerial.cpp
index b5992ad..1b1fa71 100644
--- a/cores/arduino/HardwareSerial.cpp
+++ b/cores/arduino/HardwareSerial.cpp
@@ -91,7 +91,7 @@ inline void store_char(unsigned char c, ring_buffer *buffer)
 #if !defined(USART_RX_vect) && !defined(SIG_USART0_RECV) && \
     !defined(SIG_UART0_RECV) && !defined(USART0_RX_vect) && \
 	!defined(SIG_UART_RECV)
-  #error Don't know what the Data Received vector is called for the first UART
+  #error "Don't know what the Data Received vector is called for the first UART"
 #else
   void serialEvent() __attribute__((weak));
   void serialEvent() {}
@@ -180,7 +180,7 @@ void serialEventRun(void)
 // do nothing - on the 32u4 the first USART is USART1
 #else
 #if !defined(UART0_UDRE_vect) && !defined(UART_UDRE_vect) && !defined(USART0_UDRE_vect) && !defined(USART_UDRE_vect)
-  #error Don't know what the Data Register Empty vector is called for the first UART
+  #error "Don't know what the Data Register Empty vector is called for the first UART"
 #else
 #if defined(UART0_UDRE_vect)
 ISR(UART0_UDRE_vect)
diff --git a/cores/arduino/Print.cpp b/cores/arduino/Print.cpp
index 500de8c..ff9b154 100755
--- a/cores/arduino/Print.cpp
+++ b/cores/arduino/Print.cpp
@@ -54,7 +54,7 @@ size_t Print::print(const __FlashStringHelper *ifsh)
 size_t Print::print(const String &s)
 {
   size_t n = 0;
-  for (int i = 0; i < s.length(); i++) {
+  for (uint16_t i = 0; i < s.length(); i++) {
     n += write(s[i]);
   }
   return n;
diff --git a/cores/arduino/WString.cpp b/cores/arduino/WString.cpp
index f90cef0..ad8d828 100644
--- a/cores/arduino/WString.cpp
+++ b/cores/arduino/WString.cpp
@@ -498,7 +498,7 @@ int String::lastIndexOf( char theChar ) const
 	return lastIndexOf(theChar, len - 1);
 }
 
-int String::lastIndexOf(char ch, int fromIndex) const
+int String::lastIndexOf(char ch, unsigned int fromIndex) const
 {
 	if (fromIndex >= len || fromIndex < 0) return -1;
 	char tempchar = buffer[fromIndex + 1];
@@ -514,7 +514,7 @@ int String::lastIndexOf(const String &s2) const
 	return lastIndexOf(s2, len - s2.len);
 }
 
-int String::lastIndexOf(const String &s2, int fromIndex) const
+int String::lastIndexOf(const String &s2, unsigned int fromIndex) const
 {
   	if (s2.len == 0 || len == 0 || s2.len > len || fromIndex < 0) return -1;
 	if (fromIndex >= len) fromIndex = len - 1;
@@ -522,7 +522,7 @@ int String::lastIndexOf(const String &s2, int fromIndex) const
 	for (char *p = buffer; p <= buffer + fromIndex; p++) {
 		p = strstr(p, s2.buffer);
 		if (!p) break;
-		if (p - buffer <= fromIndex) found = p - buffer;
+		if ((unsigned int)(p - buffer) <= fromIndex) found = p - buffer;
 	}
 	return found;
 }
diff --git a/cores/arduino/WString.h b/cores/arduino/WString.h
index a601aca..d76d2a3 100644
--- a/cores/arduino/WString.h
+++ b/cores/arduino/WString.h
@@ -154,9 +154,9 @@ public:
 	int indexOf( const String &str ) const;
 	int indexOf( const String &str, unsigned int fromIndex ) const;
 	int lastIndexOf( char ch ) const;
-	int lastIndexOf( char ch, int fromIndex ) const;
+	int lastIndexOf( char ch, unsigned int fromIndex ) const;
 	int lastIndexOf( const String &str ) const;
-	int lastIndexOf( const String &str, int fromIndex ) const;
+	int lastIndexOf( const String &str, unsigned int fromIndex ) const;
 	String substring( unsigned int beginIndex ) const;
 	String substring( unsigned int beginIndex, unsigned int endIndex ) const;
 
diff --git a/cores/arduino/wiring_private.h b/cores/arduino/wiring_private.h
index 74c0d06..41d1d40 100755
--- a/cores/arduino/wiring_private.h
+++ b/cores/arduino/wiring_private.h
@@ -27,7 +27,6 @@
 
 #include <avr/io.h>
 #include <avr/interrupt.h>
-#include <avr/delay.h>
 #include <stdio.h>
 #include <stdarg.h>