diff --git a/src/earcut.js b/src/earcut.js
index b4d1359..2cfd60d 100644
--- a/src/earcut.js
+++ b/src/earcut.js
@@ -483,8 +483,11 @@ function equals(p1, p2) {
 function intersects(p1, q1, p2, q2) {
     if ((equals(p1, p2) && equals(q1, q2)) ||
         (equals(p1, q2) && equals(p2, q1))) return true;
-    return area(p1, q1, p2) > 0 !== area(p1, q1, q2) > 0 &&
-           area(p2, q2, p1) > 0 !== area(p2, q2, q1) > 0;
+    var a0 = area(p1, q1, p2);
+    var a1 = area(p1, q1, q2);
+    var a2 = area(p2, q2, p1);
+    var a3 = area(p2, q2, q1);
+    return (a0 === 0 && a1 === 0) || (a0 > 0 !== a1 > 0 && a2 > 0 !== a3 > 0);
 }
 
 // check if a polygon diagonal intersects any polygon segments
diff --git a/test/expected.json b/test/expected.json
index ac018ec..7a07940 100644
--- a/test/expected.json
+++ b/test/expected.json
@@ -33,7 +33,8 @@
         "issue83": 0,
         "issue107": 0,
         "issue111": 19,
-        "boxy": 56
+        "boxy": 57,
+        "collinear-diagonal": 14
     },
     "errors": {
         "dude": 2e-15,
diff --git a/test/fixtures/collinear-diagonal.json b/test/fixtures/collinear-diagonal.json
new file mode 100644
index 0000000..87c9423
--- /dev/null
+++ b/test/fixtures/collinear-diagonal.json
@@ -0,0 +1 @@
+[[[3468,1913],[3486,1884],[3413,1869],[3322,1869],[3413,1854],[3413,1869],[3486,1869],[3486,1884],[3504,1884],[3504,1869],[3432,1869],[3432,1854],[3395,1854],[3432,1839],[3432,1854],[3450,1839],[3341,1839],[3341,1825],[3195,1825],[3341,1810],[3341,1825],[3450,1825],[3523,1854],[3523,1913]]]