diff --git a/gnu/packages/bioinformatics.scm b/gnu/packages/bioinformatics.scm
index 40dd51a3df..11d123b605 100644
--- a/gnu/packages/bioinformatics.scm
+++ b/gnu/packages/bioinformatics.scm
@@ -11882,7 +11882,8 @@ (define-public sailfish
              ;; Ensure that Eigen headers can be found
              (setenv "CPLUS_INCLUDE_PATH"
                      (string-append (assoc-ref inputs "eigen")
-                                    "/include/eigen3"))
+                                    "/include/eigen3:"
+                                    (or (getenv "CPLUS_INCLUDE_PATH") "")))
              #t)))))
     (inputs
      `(("boost" ,boost)