diff --git a/libsrc/geos-common/file/get1stdirentry.s b/libsrc/geos-common/file/get1stdirentry.s
index 3b99554eb..381a35c6d 100644
--- a/libsrc/geos-common/file/get1stdirentry.s
+++ b/libsrc/geos-common/file/get1stdirentry.s
@@ -5,7 +5,7 @@
 
 ; struct filehandle* Get1stDirEntry (void);
 
-            .import __oserror
+            .import __oserror, return0
             .export _Get1stDirEntry
 
             .include "diskdrv.inc"
@@ -14,6 +14,10 @@
 _Get1stDirEntry:
         jsr Get1stDirEntry
         stx __oserror
-        lda r5L
+        txa
+        beq L0                  ; error?
+        jmp return0             ; return NULL
+
+L0:     lda r5L
         ldx r5H
         rts
diff --git a/libsrc/geos-common/file/getnxtdirentry.s b/libsrc/geos-common/file/getnxtdirentry.s
index 912f48ca4..16a31edcf 100644
--- a/libsrc/geos-common/file/getnxtdirentry.s
+++ b/libsrc/geos-common/file/getnxtdirentry.s
@@ -5,7 +5,7 @@
 
 ; struct filehandle* GetNxtDirEntry (void);
 
-            .import __oserror
+            .import __oserror, return0
             .export _GetNxtDirEntry
 
             .include "diskdrv.inc"
@@ -14,6 +14,12 @@
 _GetNxtDirEntry:
         jsr GetNxtDirEntry
         stx __oserror
-        lda r5L
+        txa
+        beq L0                  ; error?
+        tya
+        beq L0                  ; end of dir?
+        jmp return0             ; return NULL
+
+L0:     lda r5L
         ldx r5H
         rts