diff --git a/changes.md b/changes.md
index dce41318..b0fb199c 100644
--- a/changes.md
+++ b/changes.md
@@ -1,3 +1,10 @@
+## Changes from 1.2.0 to 1.2.1
+
+#### Bugfixes
+
+* Fail when inferred source paths overlap with each other.
+  * Closes https://github.com/jonase/eastwood/issues/428
+
 ## Changes from 1.1.1 to 1.2.0
 
 #### New
diff --git a/src/eastwood/lint.clj b/src/eastwood/lint.clj
index a96cbd55..0d0f7743 100644
--- a/src/eastwood/lint.clj
+++ b/src/eastwood/lint.clj
@@ -497,6 +497,8 @@
                                         (-> s (.contains "target"))
                                         ;; https://github.com/jonase/eastwood/issues/409
                                         (-> s (.contains ".gitlibs"))))))
+                        (distinct)
+                        (util/assert-no-dir-supersets)
                         (set))
      :test-paths #{}}))
 
diff --git a/src/eastwood/util.clj b/src/eastwood/util.clj
index 58b74008..3b4c0856 100644
--- a/src/eastwood/util.clj
+++ b/src/eastwood/util.clj
@@ -1245,15 +1245,42 @@ of these kind."
        (some exclude-linters--internal)
        boolean))
 
+(defn parent-dirs-set [f]
+  (->> f
+       (iterate (fn [^File f]
+                  (some-> f .getCanonicalPath File. .getParent File.)))
+       (take-while some?)
+       (set)))
+
+(defn dir-superset? [^File candidate, other]
+  (if (->> [candidate other]
+           (map (fn [^File f]
+                  (-> f .getCanonicalPath)))
+           (apply =))
+    ;; In theory an x is a superset of itself, but we'll disregard that -
+    ;; we prefer to accept a duplicate entry over a confusing error message:
+    false
+    (boolean (some #{(-> candidate .getCanonicalPath File.)}
+                   (parent-dirs-set other)))))
+
+(defn assert-no-dir-supersets [source-paths]
+  (doseq [candidate source-paths]
+    (doseq [other (remove #{candidate} source-paths)]
+      (when (dir-superset? candidate other)
+        (throw (ex-info (format "Inferred :source-path from resource `%s` which is a superset of resource `%s`.
+Resource directories shouldn't overlap with each other, otherwise there would be an important ambiguity.
+Eastwood cannot continue."
+                                candidate
+                                other)
+                        {:superset candidate
+                         :subset other})))))
+  source-paths)
+
 (defn dir-outside-root-dir? [^File f]
   {:pre [(-> f .isDirectory)]}
   (let [f (-> f .getCanonicalPath File.)
         root-dir (File. (System/getProperty "user.dir"))
-        parent-dirs (->> f
-                         (iterate (fn [^File f]
-                                    (some-> f .getCanonicalPath File. .getParent File.)))
-                         (take-while some?)
-                         (set))]
+        parent-dirs (parent-dirs-set f)]
     (not (parent-dirs root-dir))))
 
 (defn ast->ns [ast]
diff --git a/test/eastwood/util_test.clj b/test/eastwood/util_test.clj
index 1efbc9e0..f578f358 100644
--- a/test/eastwood/util_test.clj
+++ b/test/eastwood/util_test.clj
@@ -74,3 +74,24 @@
     (File. ".")                             false
     (File. "src")                           false
     (File. "/")                             true))
+
+(deftest dir-superset?
+  (are [candidate other expected] (testing [candidate other]
+                                    (is (= expected
+                                           (sut/dir-superset? (File. candidate) (File. other))))
+                                    true)
+    "/"            "."            true
+    "/"            "src"          true
+    "/"            "src/eastwood" true
+    ;; In theory an x is a superset of itself, but we'll disregard that -
+    ;; we prefer to accept a duplicate entry over a confusing error message:
+    "/"            "/"            false
+    "."            "."            false
+    "src"          "src"          false
+    "src/eastwood" "src/eastwood" false
+
+    "."            "src"          true
+    "src"          "."            false
+    "src"          "test"         false
+    "src/eastwood" "src"          false
+    "src"          "src/eastwood" true))