diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 702ded96a3f..5e4aaf89aa1 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -242,11 +242,9 @@ namespace ts {
             const count = array.length;
             if (count > 0) {
                 let pos = 0;
-                let result = arguments.length <= 2 ? array[pos] : initial;
-                pos++;
+                let result = arguments.length <= 2 ? array[pos++] : initial;
                 while (pos < count) {
-                    result = f(<U>result, array[pos]);
-                    pos++;
+                    result = f(<U>result, array[pos++]);
                 }
                 return <U>result;
             }
@@ -260,11 +258,9 @@ namespace ts {
         if (array) {
             let pos = array.length - 1;
             if (pos >= 0) {
-                let result = arguments.length <= 2 ? array[pos] : initial;
-                pos--;
+                let result = arguments.length <= 2 ? array[pos--] : initial;
                 while (pos >= 0) {
-                    result = f(<U>result, array[pos]);
-                    pos--;
+                    result = f(<U>result, array[pos--]);
                 }
                 return <U>result;
             }