Index: ghc-8.6.1/compiler/iface/MkIface.hs
===================================================================
--- ghc-8.6.1.orig/compiler/iface/MkIface.hs
+++ ghc-8.6.1/compiler/iface/MkIface.hs
@@ -702,7 +702,7 @@ addFingerprints hsc_env mb_old_fingerpri
    iface_hash <- computeFingerprint putNameLiterally
                       (mod_hash,
                        ann_fn (mkVarOcc "module"),  -- See mkIfaceAnnCache
-                       mi_usages iface0,
+                       usages,
                        sorted_deps,
                        mi_hpc iface0)
 
@@ -737,6 +737,9 @@ addFingerprints hsc_env mb_old_fingerpri
     (non_orph_fis,   orph_fis)   = mkOrphMap ifFamInstOrph (mi_fam_insts iface0)
     fix_fn = mi_fix_fn iface0
     ann_fn = mkIfaceAnnCache (mi_anns iface0)
+    -- Do not allow filenames to affect the interface
+    usages = [ case u of UsageFile _ fp -> UsageFile "" fp; _ -> u | u <- mi_usages iface0 ]
+
 
 -- | Retrieve the orphan hashes 'mi_orphan_hash' for a list of modules
 -- (in particular, the orphan modules which are transitively imported by the