diff --git a/source/dub/package_.d b/source/dub/package_.d
index 614e196..0f3d895 100644
--- a/source/dub/package_.d
+++ b/source/dub/package_.d
@@ -441,7 +441,7 @@
 			if( !existsFile(p) ) continue;
 			foreach(fil; ["app.d", "main.d", pkg_name ~ "/main.d", pkg_name ~ "/" ~ "app.d"]){
 				if( existsFile(p ~ fil) ) {
-					app_main_file = Path(sf ~ fil).toNativeString();
+					app_main_file = (Path(sf) ~ fil).toNativeString();
 					break;
 				}
 			}
diff --git a/test/custom-source-main-bug487/.gitignore b/test/custom-source-main-bug487/.gitignore
new file mode 100644
index 0000000..433d266
--- /dev/null
+++ b/test/custom-source-main-bug487/.gitignore
@@ -0,0 +1,5 @@
+.dub
+docs.json
+__dummy.html
+*.o
+*.obj
diff --git a/test/custom-source-main-bug487/.no_run b/test/custom-source-main-bug487/.no_run
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/test/custom-source-main-bug487/.no_run
diff --git a/test/custom-source-main-bug487/.no_test b/test/custom-source-main-bug487/.no_test
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/test/custom-source-main-bug487/.no_test
diff --git a/test/custom-source-main-bug487/dub.json b/test/custom-source-main-bug487/dub.json
new file mode 100644
index 0000000..572c35c
--- /dev/null
+++ b/test/custom-source-main-bug487/dub.json
@@ -0,0 +1,6 @@
+{
+	"name": "custom-source-main-bug487",
+	"sourcePaths": ["mysrc"],
+	"dependencies": {
+	}
+}
diff --git a/test/custom-source-main-bug487/mysrc/app.d b/test/custom-source-main-bug487/mysrc/app.d
new file mode 100644
index 0000000..9198103
--- /dev/null
+++ b/test/custom-source-main-bug487/mysrc/app.d
@@ -0,0 +1,3 @@
+void main()
+{
+}