diff --git a/Fortran/gfortran/CMakeLists.txt b/Fortran/gfortran/CMakeLists.txt
--- a/Fortran/gfortran/CMakeLists.txt
+++ b/Fortran/gfortran/CMakeLists.txt
@@ -342,6 +342,10 @@
   # other diagnostics, it will be empty.
   set(out ${target}.out)
 
+  # CMake escapes spaces. To really get a space (between arguments) use a ;
+  string(REPLACE " " ";" env_fflags ${CMAKE_Fortran_FLAGS})
+  string(APPEND fflags env_fflags)
+
   add_custom_command(
     OUTPUT ${out}
     COMMAND ${CMAKE_COMMAND}