diff --git a/include/asm-um/mmu_context.h b/include/asm-um/mmu_context.h
index 7529c9c..095bb62 100644
--- a/include/asm-um/mmu_context.h
+++ b/include/asm-um/mmu_context.h
@@ -16,8 +16,12 @@
 
 #define deactivate_mm(tsk,mm)	do { } while (0)
 
+extern void force_flush_all(void);
+
 static inline void activate_mm(struct mm_struct *old, struct mm_struct *new)
 {
+	if (old != new)
+		force_flush_all();
 }
 
 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,