diff --git a/libraries/FS/src/FS.cpp b/libraries/FS/src/FS.cpp
index 8470ce1fe55..252fc3e3944 100644
--- a/libraries/FS/src/FS.cpp
+++ b/libraries/FS/src/FS.cpp
@@ -105,7 +105,7 @@ bool File::seek(uint32_t pos, SeekMode mode) {
 
 size_t File::position() const {
   if (!*this) {
-    return 0;
+    return (size_t)-1;
   }
 
   return _p->position();
diff --git a/libraries/FS/src/FS.h b/libraries/FS/src/FS.h
index 5f2a91761d2..6572ad987b3 100644
--- a/libraries/FS/src/FS.h
+++ b/libraries/FS/src/FS.h
@@ -64,7 +64,7 @@ class File : public Stream {
   bool seek(uint32_t pos) {
     return seek(pos, SeekSet);
   }
-  size_t position() const;
+  size_t position() const;  // returns (size_t)-1 on error
   size_t size() const;
   bool setBufferSize(size_t size);
   void close();