diff --git a/modules/cc.cmake b/modules/cc.cmake
index 589d75b..100efa4 100644
--- a/modules/cc.cmake
+++ b/modules/cc.cmake
@@ -21,8 +21,8 @@
 #
 #   docopt: --cc=<CC> C compiler [default: gcc].
 #           --extra-cc-flags=<EXTRA_CFLAGS> Extra C compiler flags [default: ''].
-#   export: 'CC=%s' % arguments['--cc']
-#   define: '-DEXTRA_CFLAGS="%s"' % arguments['--extra-cc-flags']
+#   export: 'CC="{0}"'.format(arguments['--cc'])
+#   define: '-DEXTRA_CFLAGS="{0}"'.format(arguments['--extra-cc-flags'])
 
 enable_language(C)
 
diff --git a/modules/cxx.cmake b/modules/cxx.cmake
index a050b2f..76bb40f 100644
--- a/modules/cxx.cmake
+++ b/modules/cxx.cmake
@@ -21,8 +21,8 @@
 #
 #   docopt: --cxx=<CXX> C++ compiler [default: g++].
 #           --extra-cxx-flags=<EXTRA_CXXFLAGS> Extra C++ compiler flags [default: ''].
-#   export: 'CXX=%s' % arguments['--cxx']
-#   define: '-DEXTRA_CXXFLAGS="%s"' % arguments['--extra-cxx-flags']
+#   export: 'CXX="{0}"'.format(arguments['--cxx'])
+#   define: '-DEXTRA_CXXFLAGS="{0}"'.format(arguments['--extra-cxx-flags'])
 
 enable_language(CXX)
 
diff --git a/modules/fc.cmake b/modules/fc.cmake
index 7169e7d..634aa33 100644
--- a/modules/fc.cmake
+++ b/modules/fc.cmake
@@ -25,8 +25,8 @@
 #
 #   docopt: --fc=<FC> Fortran compiler [default: gfortran].
 #           --extra-fc-flags=<EXTRA_FCFLAGS> Extra Fortran compiler flags [default: ''].
-#   export: 'FC=%s' % arguments['--fc']
-#   define: '-DEXTRA_FCFLAGS="%s"' % arguments['--extra-fc-flags']
+#   export: 'FC="{0}"'.format(arguments['--fc'])
+#   define: '-DEXTRA_FCFLAGS="{0}"'.format(arguments['--extra-fc-flags'])
 
 enable_language(Fortran)