diff --git a/sys/alpha/alpha/sys_machdep.c b/sys/alpha/alpha/sys_machdep.c
index 224e7e48bcfd..cc213a372c18 100644
--- a/sys/alpha/alpha/sys_machdep.c
+++ b/sys/alpha/alpha/sys_machdep.c
@@ -77,7 +77,7 @@ sysarch(td, uap)
 	struct thread *td;
 	register struct sysarch_args *uap;
 {
-	int error = 0;
+	int error;
 
 	switch(uap->op) {
 	case ALPHA_SETHAE:
diff --git a/sys/amd64/amd64/sys_machdep.c b/sys/amd64/amd64/sys_machdep.c
index b48d527005c4..e1ed61780e50 100644
--- a/sys/amd64/amd64/sys_machdep.c
+++ b/sys/amd64/amd64/sys_machdep.c
@@ -88,8 +88,9 @@ sysarch(td, uap)
 	struct thread *td;
 	register struct sysarch_args *uap;
 {
-	int error = 0;
+	int error;
 
+	mtx_lock(&Giant);
 	switch(uap->op) {
 	case I386_GET_LDT:
 		error = i386_get_ldt(td, uap->parms);
@@ -108,9 +109,10 @@ sysarch(td, uap)
 		error = vm86_sysarch(td, uap->parms);
 		break;
 	default:
-		error = EOPNOTSUPP;
+		error = EINVAL;
 		break;
 	}
+	mtx_unlock(&Giant);
 	return (error);
 }
 
diff --git a/sys/i386/i386/sys_machdep.c b/sys/i386/i386/sys_machdep.c
index b48d527005c4..e1ed61780e50 100644
--- a/sys/i386/i386/sys_machdep.c
+++ b/sys/i386/i386/sys_machdep.c
@@ -88,8 +88,9 @@ sysarch(td, uap)
 	struct thread *td;
 	register struct sysarch_args *uap;
 {
-	int error = 0;
+	int error;
 
+	mtx_lock(&Giant);
 	switch(uap->op) {
 	case I386_GET_LDT:
 		error = i386_get_ldt(td, uap->parms);
@@ -108,9 +109,10 @@ sysarch(td, uap)
 		error = vm86_sysarch(td, uap->parms);
 		break;
 	default:
-		error = EOPNOTSUPP;
+		error = EINVAL;
 		break;
 	}
+	mtx_unlock(&Giant);
 	return (error);
 }
 
diff --git a/sys/ia64/ia64/sys_machdep.c b/sys/ia64/ia64/sys_machdep.c
index 810b7d131b0c..aecae85bd55e 100644
--- a/sys/ia64/ia64/sys_machdep.c
+++ b/sys/ia64/ia64/sys_machdep.c
@@ -68,7 +68,7 @@ sysarch(td, uap)
 	struct thread *td;
 	register struct sysarch_args *uap;
 {
-	int error = 0;
+	int error;
 
 	switch(uap->op) {
 	default:
diff --git a/sys/powerpc/powerpc/sys_machdep.c b/sys/powerpc/powerpc/sys_machdep.c
index a97e2101675a..146228fd8b65 100644
--- a/sys/powerpc/powerpc/sys_machdep.c
+++ b/sys/powerpc/powerpc/sys_machdep.c
@@ -35,5 +35,5 @@ int
 sysarch(struct thread *td, struct sysarch_args *uap)
 {
 
-	return (EOPNOTSUPP);
+	return (EINVAL);
 }
diff --git a/sys/sparc64/sparc64/sys_machdep.c b/sys/sparc64/sparc64/sys_machdep.c
index 34be95acf580..d26efbb783cf 100644
--- a/sys/sparc64/sparc64/sys_machdep.c
+++ b/sys/sparc64/sparc64/sys_machdep.c
@@ -28,7 +28,9 @@
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/lock.h>
 #include <sys/malloc.h>
+#include <sys/mutex.h>
 #include <sys/proc.h>
 #include <sys/sysproto.h>
 
@@ -50,7 +52,7 @@ sysarch(struct thread *td, struct sysarch_args *uap)
 {
 	int error;
 
-	error = 0;
+	mtx_lock(&Giant);
 	switch (uap->op) {
 	case SPARC_SIGTRAMP_INSTALL:
 		error = sparc_sigtramp_install(td, uap->parms);
@@ -62,6 +64,7 @@ sysarch(struct thread *td, struct sysarch_args *uap)
 		error = EINVAL;
 		break;
 	}
+	mtx_unlock(&Giant);
 	return (error);
 }