diff --git a/src/trans/cpu/CMakeLists.txt b/src/trans/cpu/CMakeLists.txt
index 05787dcbb..cd36db8e2 100644
--- a/src/trans/cpu/CMakeLists.txt
+++ b/src/trans/cpu/CMakeLists.txt
@@ -44,9 +44,9 @@ function(generate_backend_sources)
 
   ecbuild_list_add_pattern( LIST files
     GLOB
-          algor/*
-          internal/*
-          external/*
+          algor/*.F90
+          internal/*.F90
+          external/*.F90
     QUIET
   )
 
diff --git a/src/trans/gpu/CMakeLists.txt b/src/trans/gpu/CMakeLists.txt
index 0769aa7dc..d5d62b288 100644
--- a/src/trans/gpu/CMakeLists.txt
+++ b/src/trans/gpu/CMakeLists.txt
@@ -88,8 +88,8 @@ function(generate_backend_sources)
 
   ecbuild_list_add_pattern( LIST files
     GLOB
-          internal/*
-          external/*
+          internal/*F90
+          external/*F90
     QUIET
   )
   list( APPEND files