diff --git a/.latexmkrc b/.latexmkrc
index 9325115..e7d1b48 100644
--- a/.latexmkrc
+++ b/.latexmkrc
@@ -5,7 +5,10 @@ sub mylatex {
   my $tex = "$base.tex";
 
   # Run the preprocessor
-  system('lhs2TeX', '--poly', '-o', $tex, "$base.lhs") == 0 or return $?;
+  if (-e "$base.lhs" && `which lhs2TeX` ne "") {
+    # Run the preprocessor
+    system('lhs2TeX', '--poly', '-o', $tex, "$base.lhs") == 0 or return $?;
+  }
   # Run pdflatex
   my $return = system('pdflatex', @_, $tex);
   system "echo INPUT $base.lhs >> $aux_dir1$base.fls";