diff --git a/CHANGES.md b/CHANGES.md
index e1e50262..e803d29b 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -37,6 +37,9 @@ next
 - Fix a crash when using an invalid alias name (#762, fixes #761,
   @diml)
 
+- Fix a crash when using c files from another directory (#758, fixes
+  #734, @diml)
+
 1.0+beta20 (10/04/2018)
 -----------------------
 
diff --git a/src/jbuild.ml b/src/jbuild.ml
index 55202713..f139ff31 100644
--- a/src/jbuild.ml
+++ b/src/jbuild.ml
@@ -72,6 +72,23 @@ let relative_file sexp =
     of_sexp_error sexp "relative filename expected";
   fn
 
+let c_name, cxx_name =
+  let make what ext sexp =
+    let s = string sexp in
+    if match s with
+      | "" | "." | ".."  -> true
+      | _ -> Filename.basename s <> s then
+      of_sexp_errorf sexp
+        "%S is not a valid %s name.\n\
+         Hint: To use %s files from another directory, use a \
+         (copy_files <dir>/*.c) stanza instead."
+        s what what ext
+    else
+      s
+  in
+  (make "C"   "c",
+   make "C++" "cpp")
+
 module Scope_info = struct
   module Name = struct
     type t = string option
@@ -706,8 +723,8 @@ module Library = struct
        field      "ppx_runtime_libraries" (list (located string)) ~default:[] >>= fun ppx_runtime_libraries    ->
        field_oslu "c_flags"                                                >>= fun c_flags                  ->
        field_oslu "cxx_flags"                                              >>= fun cxx_flags                ->
-       field      "c_names" (list string) ~default:[]                      >>= fun c_names                  ->
-       field      "cxx_names" (list string) ~default:[]                    >>= fun cxx_names                ->
+       field      "c_names" (list c_name) ~default:[]                      >>= fun c_names                  ->
+       field      "cxx_names" (list cxx_name) ~default:[]                  >>= fun cxx_names                ->
        field_oslu "library_flags"                                          >>= fun library_flags            ->
        field_oslu "c_library_flags"                                        >>= fun c_library_flags          ->
        field      "virtual_deps" (list (located string)) ~default:[]       >>= fun virtual_deps             ->
diff --git a/test/blackbox-tests/test-cases/github734/run.t b/test/blackbox-tests/test-cases/github734/run.t
index 43fbffc5..b4f4505a 100644
--- a/test/blackbox-tests/test-cases/github734/run.t
+++ b/test/blackbox-tests/test-cases/github734/run.t
@@ -1,28 +1,5 @@
   $ jbuilder build @foo
-  Internal error, please report upstream including the contents of _build/log.
-  Description: 
-  ("Build_system.get_collector called on closed directory"
-   (dir _build/default/src/stubs))
-  Backtrace:
-  Raised at file "src/stdune/exn.ml", line 32, characters 5-10
-  Called from file "src/build_system.ml", line 1503, characters 18-47
-  Called from file "src/gen_rules.ml", line 495, characters 4-516
-  Called from file "list.ml", line 82, characters 20-23
-  Called from file "src/gen_rules.ml", line 643, characters 8-94
-  Called from file "src/stdune/exn.ml", line 21, characters 8-11
-  Re-raised at file "src/stdune/exn.ml", line 23, characters 30-37
-  Called from file "src/gen_rules.ml", line 959, characters 13-72
-  Called from file "src/stdune/list.ml", line 13, characters 10-13
-  Called from file "src/gen_rules.ml", line 955, characters 4-777
-  Called from file "src/gen_rules.ml", line 994, characters 19-30
-  Called from file "src/build_system.ml", line 889, characters 6-62
-  Called from file "src/build_system.ml", line 865, characters 6-59
-  Re-raised at file "src/build_system.ml", line 876, characters 6-17
-  Called from file "src/build_system.ml" (inlined), line 833, characters 32-63
-  Called from file "src/build_system.ml", line 843, characters 4-24
-  Called from file "src/build_interpret.ml", line 101, characters 24-40
-  Called from file "src/build_interpret.ml", line 60, characters 31-43
-  Called from file "src/build_interpret.ml", line 60, characters 31-43
-  Called from file "src/build_system.ml", line 1215, characters 10-108
-  Called from file "src/fiber/fiber.ml", line 359, characters 6-13
+  File "src/dune", line 4, characters 12-19:
+  Error: "stubs/x" is not a valid C name.
+  Hint: To use C files from another directory, use a (copy_files <dir>/*.c) stanza instead.
   [1]