diff --git a/servers/vm/region.c b/servers/vm/region.c
index 9728bdd1c..7450fd844 100644
--- a/servers/vm/region.c
+++ b/servers/vm/region.c
@@ -1102,8 +1102,7 @@ int map_unmap_region(struct vmproc *vmp, struct vir_region *r,
 		region_remove(&vmp->vm_regions_avl, r->vaddr);
 
 		USE(r,
-		r->vaddr += len;
-		r->length -= len;);
+		r->vaddr += len;);
 
 		remslots = phys_slot(r->length);
 
@@ -1113,15 +1112,17 @@ int map_unmap_region(struct vmproc *vmp, struct vir_region *r,
 		 * point to the same addresses, make them shrink by the
 		 * same amount.
 		 */
-		for(voffset = offset; voffset < r->length;
+		for(voffset = len; voffset < r->length;
 			voffset += VM_PAGE_SIZE) {
 			if(!(pr = physblock_get(r, voffset))) continue;
 			assert(pr->offset >= offset);
+			assert(pr->offset >= len);
 			USE(pr, pr->offset -= len;);
 		}
 		if(remslots)
 			memmove(r->physblocks, r->physblocks + freeslots,
 				remslots * sizeof(struct phys_region *));
+		USE(r, r->length -= len;);
 	} else if(offset + len == r->length) {
 		assert(len <= r->length);
 		r->length -= len;
diff --git a/test/test74.c b/test/test74.c
index 8ccdaaaa0..7c7f24811 100644
--- a/test/test74.c
+++ b/test/test74.c
@@ -75,6 +75,21 @@ readblock(int b, int blocksize, u32_t seed, char *data)
 
 void testend(void) { }
 
+void basic_regression(void)
+{
+	void *block;
+#define BLOCKSIZE (PAGE_SIZE*10)
+	block = minix_mmap(0, BLOCKSIZE, PROT_READ | PROT_WRITE,
+		MAP_PRIVATE | MAP_ANON, -1, 0);
+
+	if(block == MAP_FAILED) { e(1); exit(1); }
+
+	memset(block, 0, BLOCKSIZE);
+
+	/* shrink from bottom */
+	minix_munmap(block, PAGE_SIZE);
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -82,6 +97,8 @@ main(int argc, char *argv[])
 
 	start(74);
 
+	basic_regression();
+
 	makefiles(MAXFILES);
 
 	cachequiet(!bigflag);