diff --git a/fs/dax.c b/fs/dax.c
index 131fd35ae39d..bff20cc56130 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -627,6 +627,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 		if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR))
 			goto fallback;
 
+		/*
+		 * TODO: teach vmf_insert_pfn_pmd() to support
+		 * 'pte_special' for pmds
+		 */
+		if (pfn_valid(pfn))
+			goto fallback;
+
 		if (buffer_unwritten(&bh) || buffer_new(&bh)) {
 			int i;
 			for (i = 0; i < PTRS_PER_PMD; i++)