diff --git a/assay/src/org/labkey/assay/AssayController.java b/assay/src/org/labkey/assay/AssayController.java
index 84411fb2a0c..ce1841f998f 100644
--- a/assay/src/org/labkey/assay/AssayController.java
+++ b/assay/src/org/labkey/assay/AssayController.java
@@ -762,7 +762,7 @@ public ApiResponse execute(SimpleApiJsonForm form, BindException errors) throws
                             duplicate = true;
                             FileLike newFile = AssayFileWriter.findUniqueFileName(fileName, targetDirectory);
                             newFileNames.add(i, newFile.getName());  // will infer duplication by whether an element exists at that position or not
-                            ExpData expData = ExperimentService.get().getExpDataByURL(f.toURI().toString(), null);
+                            ExpData expData = ExperimentService.get().getExpDataByURL(f.toNioPathForRead().toFile(), null);
                             List<String> runNames = new ArrayList<>();
                             if (expData != null)
                             {