diff --git a/src/Effect/Aff.js b/src/Effect/Aff.js
index 190216e..a44656e 100644
--- a/src/Effect/Aff.js
+++ b/src/Effect/Aff.js
@@ -274,12 +274,18 @@ var Aff = function () {
         switch (status) {
         case STEP_BIND:
           status = CONTINUE;
-          step   = bhead(step);
-          if (btail === null) {
-            bhead = null;
-          } else {
-            bhead = btail._1;
-            btail = btail._2;
+          try {
+            step   = bhead(step);
+            if (btail === null) {
+              bhead = null;
+            } else {
+              bhead = btail._1;
+              btail = btail._2;
+            }
+          } catch (e) {
+            status = RETURN;
+            fail   = util.left(e);
+            step   = null;
           }
           break;