diff --git a/src/source_terms/source_term_handler.f90 b/src/source_terms/source_term_handler.f90
index b9163c80180..9b3c7110107 100644
--- a/src/source_terms/source_term_handler.f90
+++ b/src/source_terms/source_term_handler.f90
@@ -225,7 +225,12 @@ subroutine source_term_handler_add_source_term(this, source_term)
 
     integer :: n_sources, i
 
-    n_sources = size(this%source_terms)
+    if(allocated(this%source_terms)) then
+       n_sources = size(this%source_terms)
+    else
+       n_sources = 0
+    endif
+
     call move_alloc(this%source_terms, temp)
     allocate(this%source_terms(n_sources + 1))