diff --git a/graph-lib/Makefile b/graph-lib/Makefile
index 56272f34..b741a597 100644
--- a/graph-lib/Makefile
+++ b/graph-lib/Makefile
@@ -7,7 +7,7 @@ make/make: make/make.rkt make/lib.rkt
 
 .PHONY: clean
 clean:
-	rm -fr make/make docs coverage
+	rm -fr make/make docs
 	find \( -path ./lib/doc/bracket -prune -and -false \) -or -name compiled -print0 | xargs -0 rm -rf
 
 .PHONY: build-dep
diff --git a/graph-lib/make/lib.rkt b/graph-lib/make/lib.rkt
index c6886765..fe0bdf8e 100644
--- a/graph-lib/make/lib.rkt
+++ b/graph-lib/make/lib.rkt
@@ -226,12 +226,12 @@
                                 " "))
         (display "\033[1;34m")
         (flush-output)
-        (let ((result (apply system* arg0 args)))
+        (let ((exit-code (apply system*/exit-code arg0 args)))
           (display "\033[m")
           (flush-output)
-          (unless result
-            (raise "Command failed."))
-          result))))
+          (unless (= exit-code 0)
+            (raise (format "Command failed with exit code ~a." exit-code)))
+          (= exit-code 0)))))
 
 (define-syntax-rule (run! . rest) (let () (run . rest) (values)))
 
@@ -253,4 +253,4 @@
     (case-lambda
       [(x) (fn x 'none 'none)]
       [(x a) (fn x a 'none)]
-      [(x a b) (fn x a (list b))])))
\ No newline at end of file
+      [(x a b) (fn x a (list b))])))
diff --git a/graph-lib/make/make.rkt b/graph-lib/make/make.rkt
index c592fb9e..28ca16c4 100644
--- a/graph-lib/make/make.rkt
+++ b/graph-lib/make/make.rkt
@@ -137,7 +137,7 @@
 
 (run! `(,(find-executable-path-or-fail "raco")
         "make"
-        "-j" "8"
+        "-j" "5"
         ,@rkt-files))
 
 ;; Create root MathJax link, must be done before the others