diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index c82a82eb539325c913b5d4d7720c1d1083e0a1f0..db73bc9e3fa25ab3beea6440d7dd68d391bd3172 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -428,64 +428,70 @@ static void kmalloc_uaf_16(struct kunit *test)
 	kfree(ptr1);
 }
 
+/*
+ * Note: in the memset tests below, the written range touches both valid and
+ * invalid memory. This makes sure that the instrumentation does not only check
+ * the starting address but the whole range.
+ */
+
 static void kmalloc_oob_memset_2(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 8;
+	size_t size = 128 - KASAN_GRANULE_SIZE;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
-	KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + 7 + OOB_TAG_OFF, 0, 2));
+	KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 1, 0, 2));
 	kfree(ptr);
 }
 
 static void kmalloc_oob_memset_4(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 8;
+	size_t size = 128 - KASAN_GRANULE_SIZE;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
-	KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + 5 + OOB_TAG_OFF, 0, 4));
+	KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 3, 0, 4));
 	kfree(ptr);
 }
 
-
 static void kmalloc_oob_memset_8(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 8;
+	size_t size = 128 - KASAN_GRANULE_SIZE;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
-	KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + 1 + OOB_TAG_OFF, 0, 8));
+	KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 7, 0, 8));
 	kfree(ptr);
 }
 
 static void kmalloc_oob_memset_16(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 16;
+	size_t size = 128 - KASAN_GRANULE_SIZE;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
-	KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + 1 + OOB_TAG_OFF, 0, 16));
+	KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 15, 0, 16));
 	kfree(ptr);
 }
 
 static void kmalloc_oob_in_memset(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 666;
+	size_t size = 128 - KASAN_GRANULE_SIZE;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
-	KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr, 0, size + 5 + OOB_TAG_OFF));
+	KUNIT_EXPECT_KASAN_FAIL(test,
+				memset(ptr, 0, size + KASAN_GRANULE_SIZE));
 	kfree(ptr);
 }