diff --git a/sys/boot/common/crc32.c b/sys/boot/common/crc32.c
index 1a3e3a3..62d9bed 100644
--- a/sys/boot/common/crc32.c
+++ b/sys/boot/common/crc32.c
@@ -42,10 +42,8 @@
  * CRC32 code derived from work by Gary S. Brown.
  */
 
-#include <sys/cdefs.h>
-__FBSDID("$FreeBSD$");
-
-#include <sys/types.h>
+#include <stddef.h>
+#include <stdint.h>
 
 #include "crc32.h"
 
@@ -96,12 +94,13 @@ static const uint32_t crc32_tab[] = {
 };
 
 uint32_t
-crc32(const void *buf, size_t size)
+crc32(uint32_t crc, const void *buf, size_t size)
 {
-	const uint8_t *p = buf;
-	uint32_t crc;
+	const uint8_t *p;
+
+	p = buf;
+	crc = (crc ^ ~0U);
 
-	crc = ~0U;
 	while (size--)
 		crc = crc32_tab[(crc ^ *p++) & 0xFF] ^ (crc >> 8);
 	return (crc ^ ~0U);
diff --git a/sys/boot/common/crc32.h b/sys/boot/common/crc32.h
index adfd628..19fdd50 100644
--- a/sys/boot/common/crc32.h
+++ b/sys/boot/common/crc32.h
@@ -8,6 +8,18 @@
 #ifndef _CRC32_H_
 #define	_CRC32_H_
 
-uint32_t crc32(const void *buf, size_t size);
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+uint32_t crc32(uint32_t crc, const void *buf, size_t size);
+
+#ifdef __cplusplus
+}
+#endif
 
 #endif	/* !_CRC32_H_ */