diff --git a/tools/makeparallel/Makefile b/tools/makeparallel/Makefile
index 4e12b10..82a4abf 100644
--- a/tools/makeparallel/Makefile
+++ b/tools/makeparallel/Makefile
@@ -65,8 +65,9 @@
 makeparallel_test: $(MAKEPARALLEL)
 	@EXPECTED="-j1234" $(MAKEPARALLEL_TEST) -j1234
 	@EXPECTED="-j123"  $(MAKEPARALLEL_TEST) -j123
-	@EXPECTED="-j1"    $(MAKEPARALLEL_TEST) -j1
-	@EXPECTED="-j1"    $(MAKEPARALLEL_TEST)
+	@EXPECTED=""       $(MAKEPARALLEL_TEST) -j1
+	@EXPECTED="-j$$(($$(nproc) + 2))"   $(MAKEPARALLEL_TEST) -j
+	@EXPECTED=""       $(MAKEPARALLEL_TEST)
 
 	@EXPECTED="-j1234" $(MAKEPARALLEL_NINJA_TEST) -j1234
 	@EXPECTED="-j123"  $(MAKEPARALLEL_NINJA_TEST) -j123
@@ -87,8 +88,6 @@
 	@EXPECTED="-j1234 -k0" $(MAKEPARALLEL_NINJA_TEST) -j1234 -k
 	@EXPECTED="-j1234 -k0" $(MAKEPARALLEL_NINJA_TEST) -kt -j1234
 
-	@EXPECTED="-j1"    $(MAKEPARALLEL_TEST) A=-j1234
-	@EXPECTED="-j1"    $(MAKEPARALLEL_TEST) A\ -j1234=-j1234
-	@EXPECTED="-j1234" $(MAKEPARALLEL_TEST) A\ -j1234=-j1234 -j1234
+	@EXPECTED=""       $(MAKEPARALLEL_TEST) A=-j1234
 
 	@EXPECTED="-j1234 args" ARGS="args" $(MAKEPARALLEL_TEST) -j1234
diff --git a/tools/makeparallel/makeparallel.cpp b/tools/makeparallel/makeparallel.cpp
index 4ae8f61..b906681 100644
--- a/tools/makeparallel/makeparallel.cpp
+++ b/tools/makeparallel/makeparallel.cpp
@@ -317,13 +317,27 @@
     }
   }
 
-  std::string jarg = "-j" + std::to_string(tokens + 1);
+  std::string jarg;
+  if (parallel) {
+    if (tokens == 0) {
+      if (ninja) {
+        // ninja is parallel by default
+        jarg = "";
+      } else {
+        // make -j with no argument, guess a reasonable parallelism like ninja does
+        jarg = "-j" + std::to_string(sysconf(_SC_NPROCESSORS_ONLN) + 2);
+      }
+    } else {
+      jarg = "-j" + std::to_string(tokens + 1);
+    }
+  }
+
 
   if (ninja) {
     if (!parallel) {
       // ninja is parallel by default, pass -j1 to disable parallelism if make wasn't parallel
       args.push_back(strdup("-j1"));
-    } else if (tokens > 0) {
+    } else {
       args.push_back(strdup(jarg.c_str()));
     }
     if (keep_going) {