diff --git a/fs/dax.c b/fs/dax.c
index d1e5cb7..43671b6 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -541,6 +541,10 @@
 	unsigned long pfn;
 	int result = 0;
 
+	/* dax pmd mappings are broken wrt gup and fork */
+	if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
+		return VM_FAULT_FALLBACK;
+
 	/* Fall back to PTEs if we're going to COW */
 	if (write && !(vma->vm_flags & VM_SHARED))
 		return VM_FAULT_FALLBACK;