diff --git a/kernel/syscall.c b/kernel/syscall.c
index 8710a827..be321bc1 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -316,6 +316,7 @@ out:
 SYSCALL_DECLARE(mmap)
 {
 	const int supported_flags = 0
+		| MAP_SHARED		// 01
 		| MAP_PRIVATE		// 02
 		| MAP_FIXED		// 10
 		| MAP_ANONYMOUS		// 20
@@ -329,7 +330,6 @@ SYSCALL_DECLARE(mmap)
 		| MAP_STACK		// 00020000
 		;
 	const int error_flags = 0
-		| MAP_SHARED		// 01
 #ifndef	USE_NOCACHE_MMAP
 		| MAP_32BIT		// 40
 #endif /* ndef USE_NOCACHE_MMAP */
@@ -410,6 +410,14 @@ SYSCALL_DECLARE(mmap)
 		goto out;
 	}
 
+	if ((flags & MAP_SHARED) && !(flags & MAP_ANONYMOUS)) {
+		ekprintf("sys_mmap(%lx,%lx,%x,%x,%x,%lx):NYI:shared mapped file%lx\n",
+				addr0, len0, prot, flags, fd, off,
+				(flags & ~(supported_flags | ignored_flags)));
+		error = -EINVAL;
+		goto out;
+	}
+
 	ihk_mc_spinlock_lock_noirq(&proc->vm->memory_range_lock);
 
 	if (flags & MAP_FIXED) {