diff --git a/src/Layout.js b/src/Layout.js
index 99a52cee..4f99754a 100755
--- a/src/Layout.js
+++ b/src/Layout.js
@@ -361,7 +361,7 @@ var computeLayout = (function() {
     var/*float*/ leadingMainDim = 0;
     var/*float*/ betweenMainDim = 0;
 
-    var/*float*/ definedMainDim = 0;
+    var/*float*/ definedMainDim = fmaxf(mainContentDim, 0);
     if (!isUndefined(node.layout[dim[mainAxis]])) {
       definedMainDim = node.layout[dim[mainAxis]];
     }
@@ -373,7 +373,7 @@ var computeLayout = (function() {
 
     // If there are flexible children in the mix, they are going to fill the
     // remaining space
-    if (flexibleChildrenCount != 0) {
+    if (flexibleChildrenCount !== 0) {
       var/*float*/ flexibleMainDim = remainingMainDim / totalFlexible;
 
       // The non flexible children can overflow the container, in this case
diff --git a/src/__tests__/Layout-test.js b/src/__tests__/Layout-test.js
index bf8b29ac..8893f9b1 100755
--- a/src/__tests__/Layout-test.js
+++ b/src/__tests__/Layout-test.js
@@ -1055,17 +1055,6 @@ describe('Layout', function() {
     );
   });
 
-  it('should layout negative margin top and center justify content', function() {
-    testLayout(
-      {style: {justifyContent: 'center'}, children: [
-        {style: {marginTop: -6}}
-      ]},
-      {width: 0, height: 0, top: 0, left: 0, children: [
-        {width: 0, height: 0, top: -3, left: 0}
-      ]}
-    );
-  });
-
   it('should layout border bottom inside of justify content space between container', function() {
     testLayout(
       {style: {justifyContent: 'space-between'}, children: [
@@ -1077,6 +1066,29 @@ describe('Layout', function() {
     );
   });
 
+  it('should layout negative margin top inside of justify content center container', function() {
+    testLayout(
+      {style: {justifyContent: 'center'}, children: [
+        {style: {marginTop: -6}}
+      ]},
+      {width: 0, height: 0, top: 0, left: 0, children: [
+        {width: 0, height: 0, top: -3, left: 0}
+      ]}
+    );
+  });
+
+  it('should layout positive margin top inside of justify content center container', function() {
+    testLayout(
+      {style: {justifyContent: 'center'}, children: [
+        {style: {marginTop: 20}}
+      ]},
+      {width: 0, height: 20, top: 0, left: 0, children: [
+        {width: 0, height: 0, top: 20, left: 0}
+      ]}
+    );
+  });
+
+
   xit('should layout flex-wrap', function() {
     testLayout(
       {style: {flexWrap: 'wrap', flexDirection: 'row', width: 100}, children: [