diff --git a/libcpuid/libcpuid.h b/libcpuid/libcpuid.h
index 224138f..257b99e 100644
--- a/libcpuid/libcpuid.h
+++ b/libcpuid/libcpuid.h
@@ -857,7 +857,7 @@ struct msr_driver_t* cpu_msr_driver_open_core(int core_num);
  *          The error message can be obtained by calling \ref cpuid_error.
  *          @see cpu_error_t
  */
-int cpu_rdmsr(struct msr_driver_t* handle, int msr_index, uint64_t* result);
+int cpu_rdmsr(struct msr_driver_t* handle, uint32_t msr_index, uint64_t* result);
 
 
 typedef enum {
diff --git a/libcpuid/rdmsr.c b/libcpuid/rdmsr.c
index 2aee872..ebc73a8 100644
--- a/libcpuid/rdmsr.c
+++ b/libcpuid/rdmsr.c
@@ -105,7 +105,7 @@ struct msr_driver_t* cpu_msr_driver_open_core(int core_num)
 	handle->fd = fd;
 	return handle;
 }
-int cpu_rdmsr(struct msr_driver_t* driver, int msr_index, uint64_t* result)
+int cpu_rdmsr(struct msr_driver_t* driver, uint32_t msr_index, uint64_t* result)
 {
 	ssize_t ret;
 
@@ -350,7 +350,7 @@ clean_up:
 #define IOCTL_UNKNOWN_BASE              FILE_DEVICE_UNKNOWN
 #define IOCTL_PROCVIEW_RDMSR			CTL_CODE(IOCTL_UNKNOWN_BASE, 0x0803, METHOD_BUFFERED, FILE_READ_ACCESS | FILE_WRITE_ACCESS)
 
-int cpu_rdmsr(struct msr_driver_t* driver, int msr_index, uint64_t* result)
+int cpu_rdmsr(struct msr_driver_t* driver, uint32_t msr_index, uint64_t* result)
 {
 	DWORD dwBytesReturned;
 	__int64 msrdata;