--- src/config/discover.ml.orig
+++ src/config/discover.ml
@@ -26,7 +26,8 @@
           { libs = [ "-lgsl"; "-lgslcblas"; "-lm" ]; cflags = [] }
         in
         let write_gsl_include = C.Flags.write_lines "gsl_include.sexp" in
-        let default_gsl_include = [ "/usr/include" ] in
+        let default_gsl_include =
+          [ (try Sys.getenv "GSL_INCLUDE_DIR" with Not_found -> "/usr/include") ] in
         match C.Pkg_config.get c with
         | None ->
             write_gsl_include default_gsl_include;