diff --git a/src/source.f90 b/src/source.f90
index edc262c5fa..1cadd571cb 100644
--- a/src/source.f90
+++ b/src/source.f90
@@ -126,7 +126,7 @@ contains
     p => source_bank(source_index)
 
     ! set uid
-    p % uid = bank_first + source_index
+    p % uid = bank_first + source_index - 1
 
   end function get_source_particle