diff --git a/sys/kern/kern_prot.c b/sys/kern/kern_prot.c
--- a/sys/kern/kern_prot.c
+++ b/sys/kern/kern_prot.c
@@ -288,7 +288,7 @@
 
 #ifndef _SYS_SYSPROTO_H_
 struct getgroups_args {
-	u_int	gidsetsize;
+	int	gidsetsize;
 	gid_t	*gidset;
 };
 #endif
@@ -296,8 +296,7 @@
 sys_getgroups(struct thread *td, struct getgroups_args *uap)
 {
 	struct ucred *cred;
-	u_int ngrp;
-	int error;
+	int ngrp, error;
 
 	cred = td->td_ucred;
 	ngrp = cred->cr_ngroups;
@@ -791,7 +790,7 @@
 
 #ifndef _SYS_SYSPROTO_H_
 struct setgroups_args {
-	u_int	gidsetsize;
+	int	gidsetsize;
 	gid_t	*gidset;
 };
 #endif
@@ -801,11 +800,10 @@
 {
 	gid_t smallgroups[XU_NGROUPS];
 	gid_t *groups;
-	u_int gidsetsize;
-	int error;
+	int gidsetsize, error;
 
 	gidsetsize = uap->gidsetsize;
-	if (gidsetsize > ngroups_max + 1)
+	if (gidsetsize > ngroups_max + 1 || gidsetsize < 0)
 		return (EINVAL);
 
 	if (gidsetsize > XU_NGROUPS)
diff --git a/sys/kern/syscalls.master b/sys/kern/syscalls.master
--- a/sys/kern/syscalls.master
+++ b/sys/kern/syscalls.master
@@ -523,13 +523,13 @@
 	}
 79	AUE_GETGROUPS	STD {
 		int getgroups(
-		    u_int gidsetsize,
+		    int gidsetsize,
 		    _Out_writes_opt_(gidsetsize) gid_t *gidset
 		);
 	}
 80	AUE_SETGROUPS	STD {
 		int setgroups(
-		    u_int gidsetsize,
+		    int gidsetsize,
 		    _In_reads_(gidsetsize) gid_t *gidset
 		);
 	}