diff --git a/src/SparkFunSX1509.cpp b/src/SparkFunSX1509.cpp
index 01b0dd9..702619b 100644
--- a/src/SparkFunSX1509.cpp
+++ b/src/SparkFunSX1509.cpp
@@ -676,7 +676,7 @@ void SX1509::configClock(uint8_t oscSource /*= 2*/, uint8_t oscPinFunction /*= 0
 	writeByte(REG_MISC, regMisc);
 }
 
-uint8_t SX1509::calculateLEDTRegister(uint8_t ms)
+uint8_t SX1509::calculateLEDTRegister(unsigned long ms)
 {
 	uint8_t regOn1, regOn2;
 	float timeOn1, timeOn2;
@@ -698,7 +698,7 @@ uint8_t SX1509::calculateLEDTRegister(uint8_t ms)
 		return regOn2;
 }
 
-uint8_t SX1509::calculateSlopeRegister(uint8_t ms, uint8_t onIntensity, uint8_t offIntensity)
+uint8_t SX1509::calculateSlopeRegister(unsigned long ms, uint8_t onIntensity, uint8_t offIntensity)
 {
 	uint16_t regSlope1, regSlope2;
 	float regTime1, regTime2;
diff --git a/src/SparkFunSX1509.h b/src/SparkFunSX1509.h
index b85cdc4..7011223 100644
--- a/src/SparkFunSX1509.h
+++ b/src/SparkFunSX1509.h
@@ -75,10 +75,10 @@ class SX1509
 	// Helper functions:
 	// calculateLEDTRegister - Try to estimate an LED on/off duration register,
 	// given the number of milliseconds and LED clock frequency.
-	uint8_t calculateLEDTRegister(uint8_t ms);
+	uint8_t calculateLEDTRegister(unsigned long ms);
 	// calculateSlopeRegister - Try to estimate an LED rise/fall duration
 	// register, given the number of milliseconds and LED clock frequency.
-	uint8_t calculateSlopeRegister(uint8_t ms, uint8_t onIntensity, uint8_t offIntensity);
+	uint8_t calculateSlopeRegister(unsigned long ms, uint8_t onIntensity, uint8_t offIntensity);
 
 public:
 	// -----------------------------------------------------------------------------