diff --git a/cgo/sha1_nix.go b/cgo/sha1_nix.go
index 144e48b..b775a18 100644
--- a/cgo/sha1_nix.go
+++ b/cgo/sha1_nix.go
@@ -16,7 +16,7 @@ func (d *digest) Write(p []byte) (nn int, err error) {
 	}
 
 	data := (*C.char)(unsafe.Pointer(&p[0]))
-	C.SHA1DCUpdate(&d.ctx, data, (C.ulong)(len(p)))
+	C.SHA1DCUpdate(&d.ctx, data, (C.size_t)(len(p)))
 
 	return len(p), nil
 }
diff --git a/cgo/sha1_nix_armhf.go b/cgo/sha1_nix_armhf.go
index 10aa8ca..5b7a725 100644
--- a/cgo/sha1_nix_armhf.go
+++ b/cgo/sha1_nix_armhf.go
@@ -16,7 +16,7 @@ func (d *digest) Write(p []byte) (nn int, err error) {
 	}
 
 	data := (*C.char)(unsafe.Pointer(&p[0]))
-	C.SHA1DCUpdate(&d.ctx, data, (C.uint)(len(p)))
+	C.SHA1DCUpdate(&d.ctx, data, (C.size_t)(len(p)))
 
 	return len(p), nil
 }
diff --git a/cgo/sha1_windows.go b/cgo/sha1_windows.go
index 3743b96..c179985 100644
--- a/cgo/sha1_windows.go
+++ b/cgo/sha1_windows.go
@@ -16,7 +16,7 @@ func (d *digest) Write(p []byte) (nn int, err error) {
 	}
 
 	data := (*C.char)(unsafe.Pointer(&p[0]))
-	C.SHA1DCUpdate(&d.ctx, data, (C.ulonglong)(len(p)))
+	C.SHA1DCUpdate(&d.ctx, data, (C.size_t)(len(p)))
 
 	return len(p), nil
 }