diff --git a/config.default.h b/config.default.h
index 4be4df2..db5c6d1 100644
--- a/config.default.h
+++ b/config.default.h
@@ -35,7 +35,7 @@
 	CPU clock rate
 */
 #ifndef	F_CPU
-	#define	F_CPU	16000000L
+	#define	F_CPU	16000000UL
 #endif
 
 /** \def HOST
diff --git a/config.gen3.h b/config.gen3.h
index 72a4b2e..f9c5965 100644
--- a/config.gen3.h
+++ b/config.gen3.h
@@ -37,7 +37,7 @@
 	CPU clock rate
 */
 #ifndef	F_CPU
-	#define	F_CPU	16000000L
+	#define	F_CPU	16000000UL
 #endif
 
 /** \def HOST
diff --git a/config.gen6.h b/config.gen6.h
index 2ae4631..04ed635 100644
--- a/config.gen6.h
+++ b/config.gen6.h
@@ -37,7 +37,7 @@
 	CPU clock rate
 */
 #ifndef	F_CPU
-	#define	F_CPU	16000000L
+	#define	F_CPU	16000000UL
 #endif
 
 /** \def HOST
diff --git a/config.gen7.h b/config.gen7.h
index 9ce617a..9f804a7 100644
--- a/config.gen7.h
+++ b/config.gen7.h
@@ -40,7 +40,7 @@
 	CPU clock rate
 */
 #ifndef	F_CPU
-	#define	F_CPU	20000000L
+	#define	F_CPU	20000000UL
 #endif
 
 /** \def HOST
diff --git a/config.ramps-v1.2.h b/config.ramps-v1.2.h
index ce5b583..02f0da8 100644
--- a/config.ramps-v1.2.h
+++ b/config.ramps-v1.2.h
@@ -37,7 +37,7 @@
 	CPU clock rate
 */
 #ifndef	F_CPU
-	#define	F_CPU	16000000L
+	#define	F_CPU	16000000UL
 #endif
 
 /** \def HOST
diff --git a/config.ramps-v1.3.h b/config.ramps-v1.3.h
index ba79455..43862e0 100644
--- a/config.ramps-v1.3.h
+++ b/config.ramps-v1.3.h
@@ -37,7 +37,7 @@
 	CPU clock rate
 */
 #ifndef	F_CPU
-	#define	F_CPU	16000000L
+	#define	F_CPU	16000000UL
 #endif
 
 /** \def HOST
diff --git a/config.sanguinololu-v1.1.h b/config.sanguinololu-v1.1.h
index 227577c..26aeaa1 100644
--- a/config.sanguinololu-v1.1.h
+++ b/config.sanguinololu-v1.1.h
@@ -36,7 +36,7 @@
 	CPU clock rate
 */
 #ifndef	F_CPU
-	#define	F_CPU	16000000L
+	#define	F_CPU	16000000UL
 #endif
 
 /** \def HOST
diff --git a/config.sanguinololu-v1.2.h b/config.sanguinololu-v1.2.h
index 9b51e42..342aa1f 100644
--- a/config.sanguinololu-v1.2.h
+++ b/config.sanguinololu-v1.2.h
@@ -36,7 +36,7 @@
 	CPU clock rate
 */
 #ifndef	F_CPU
-	#define	F_CPU	16000000L
+	#define	F_CPU	16000000UL
 #endif
 
 /** \def HOST