diff --git a/esmvalcore/preprocessor/_mask.py b/esmvalcore/preprocessor/_mask.py
index 88c09de9ad..1f363096ee 100644
--- a/esmvalcore/preprocessor/_mask.py
+++ b/esmvalcore/preprocessor/_mask.py
@@ -688,6 +688,7 @@ def mask_fillvalues(
                 combined_mask,
             )
 
+    input_products = {p.copy_provenance() for p in products}
     for product in products:
         for cube in product.cubes:
             array = cube.core_data()
@@ -695,11 +696,10 @@ def mask_fillvalues(
             mask = array_module.ma.getmaskarray(array) | combined_mask
             cube.data = array_module.ma.masked_array(data, mask)
 
-    # Record provenance
-    input_products = {p.copy_provenance() for p in products}
-    for other in input_products:
-        if other.filename != product.filename:
-            product.wasderivedfrom(other)
+        # Record provenance
+        for other in input_products:
+            if other.filename != product.filename:
+                product.wasderivedfrom(other)
 
     return products