diff --git a/lib/envars.ml b/lib/envars.ml
index b5036e73403ec..f68b9828bb295 100644
--- a/lib/envars.ml
+++ b/lib/envars.ml
@@ -12,7 +12,13 @@ open Util
 
 (** {1 Helper functions} *)
 
-let getenv_else s dft = try Sys.getenv s with Not_found -> dft ()
+let getenv_else s dft =
+  try
+    let v = Sys.getenv s in
+    if String.equal v ""
+    then dft ()
+    else v
+  with Not_found -> dft ()
 
 let safe_getenv warning n =
   getenv_else n (fun () ->
diff --git a/tools/CoqMakefile.in b/tools/CoqMakefile.in
index b673225e409a4..914269cd78172 100644
--- a/tools/CoqMakefile.in
+++ b/tools/CoqMakefile.in
@@ -33,7 +33,13 @@ COQLIBS           := $(COQMF_COQLIBS)
 COQLIBS_NOML      := $(COQMF_COQLIBS_NOML)
 CMDLINE_COQLIBS   := $(COQMF_CMDLINE_COQLIBS)
 LOCAL             := $(COQMF_LOCAL)
-COQLIB            := $(COQMF_COQLIB)
+# We add a workaround for #8731; if COQLIB is set externally, don't
+# override it.
+ifeq ($(COQMF_COQLIB),)
+   COQLIB := $(shell coqtop -where)/
+else
+   COQLIB := $(COQMF_COQLIB)
+endif
 DOCDIR            := $(COQMF_DOCDIR)
 OCAMLFIND         := $(COQMF_OCAMLFIND)
 CAMLFLAGS         := $(COQMF_CAMLFLAGS)