diff --git a/tests/issue3070/dub.json b/tests/issue3070/dub.json
new file mode 100644
index 000000000..1ff76e84c
--- /dev/null
+++ b/tests/issue3070/dub.json
@@ -0,0 +1,7 @@
+{
+  "name": "issue3070",
+  "description": "Test mixed path separators do not duplicate mainSourceFile",
+  "targetType": "executable",
+  "sourcePaths": ["src"],
+  "mainSourceFile": "src/main.d"
+}
diff --git a/tests/issue3070/src/main.d b/tests/issue3070/src/main.d
new file mode 100644
index 000000000..a74017975
--- /dev/null
+++ b/tests/issue3070/src/main.d
@@ -0,0 +1 @@
+void main() {}
diff --git a/tests/run.d b/tests/run.d
new file mode 100644
index 000000000..668d410c8
--- /dev/null
+++ b/tests/run.d
@@ -0,0 +1,2 @@
+runDubTest("issue3070");
+runDubTest("issue3070");