diff --git a/var/spack/repos/builtin/packages/gsl/package.py b/var/spack/repos/builtin/packages/gsl/package.py
index 21d7bd63716..dd5bad19cd8 100644
--- a/var/spack/repos/builtin/packages/gsl/package.py
+++ b/var/spack/repos/builtin/packages/gsl/package.py
@@ -55,3 +55,8 @@ def configure_args(self):
             configure_args.append("CBLAS_LIBS=%s" % self.spec["blas"].libs.ld_flags)
 
         return configure_args
+
+    def setup_run_environment(self, env):
+        # cmake looks for GSL_ROOT_DIR to find GSL so this helps pick the spack one
+        # when there are multiple installations (e.g. a system one and a spack one)
+        env.set("GSL_ROOT_DIR", self.prefix)