diff --git a/AsyncDisplayKit/ASDisplayNode.mm b/AsyncDisplayKit/ASDisplayNode.mm
index 3bfe80760c..850d0a46aa 100644
--- a/AsyncDisplayKit/ASDisplayNode.mm
+++ b/AsyncDisplayKit/ASDisplayNode.mm
@@ -1704,7 +1704,7 @@ static NSInteger incrementIfFound(NSInteger i) {
   }
     
   if ([newSupernode supportsUpwardPropagation]) {
-    ASEnvironmentStatePropagateUp(newSupernode, self.environmentState.layoutOptionsState);
+    ASEnvironmentStatePropagateUp(newSupernode, _environmentState.layoutOptionsState);
   }
 }
 
diff --git a/AsyncDisplayKit/Details/ASEnvironment.h b/AsyncDisplayKit/Details/ASEnvironment.h
index 43e21bda09..62e352fb52 100644
--- a/AsyncDisplayKit/Details/ASEnvironment.h
+++ b/AsyncDisplayKit/Details/ASEnvironment.h
@@ -48,7 +48,6 @@ typedef struct ASEnvironmentLayoutOptionsState {
   
   ASEnvironmentStateExtensions _extensions;
 } ASEnvironmentLayoutOptionsState;
-extern ASEnvironmentLayoutOptionsState ASEnvironmentLayoutOptionsStateCreate();
 
 
 #pragma mark - ASEnvironmentHierarchyState
@@ -59,7 +58,6 @@ typedef struct ASEnvironmentHierarchyState {
   unsigned transitioningSupernodes:1; // = NO
   unsigned layoutPending:1; // = NO
 } ASEnvironmentHierarchyState;
-extern ASEnvironmentHierarchyState ASEnvironmentHierarchyStateCreate();
 
 
 #pragma mark - ASEnvironmentState
@@ -92,6 +90,7 @@ ASDISPLAYNODE_EXTERN_C_END
 /// Returns all children of an object which class conforms to the ASEnvironment protocol
 - (NSArray<id<ASEnvironment>> *)children;
 
+/// Classes should implement this method and return YES / NO dependent if upward propagation is enabled or not 
 - (BOOL)supportsUpwardPropagation;
 
 @end
diff --git a/AsyncDisplayKit/Details/ASEnvironment.m b/AsyncDisplayKit/Details/ASEnvironment.m
index 5cbe4d95c1..01006405d4 100644
--- a/AsyncDisplayKit/Details/ASEnvironment.m
+++ b/AsyncDisplayKit/Details/ASEnvironment.m
@@ -10,32 +10,24 @@
 
 #import "ASEnvironment.h"
 
-ASEnvironmentLayoutOptionsState ASEnvironmentLayoutOptionsStateCreate()
+ASEnvironmentLayoutOptionsState _ASEnvironmentLayoutOptionsStateCreate()
 {
   return (ASEnvironmentLayoutOptionsState) {
-    .spacingBefore = 0,
-    .flexBasis = ASRelativeDimensionUnconstrained,
-    .alignSelf = ASStackLayoutAlignSelfAuto,
-    
-    .sizeRange = ASRelativeSizeRangeMake(ASRelativeSizeMakeWithCGSize(CGSizeZero), ASRelativeSizeMakeWithCGSize(CGSizeZero)),
-    .layoutPosition = CGPointZero
+    // Default values can be defined in here
   };
 }
 
-ASEnvironmentHierarchyState ASEnvironmentHierarchyStateCreate()
+ASEnvironmentHierarchyState _ASEnvironmentHierarchyStateCreate()
 {
   return (ASEnvironmentHierarchyState) {
-    .rasterized = NO,
-    .rangeManaged = NO,
-    .transitioningSupernodes = NO,
-    .layoutPending = NO
+    // Default values can be defined in here
   };
 }
 
 ASEnvironmentState ASEnvironmentStateCreate()
 {
   return (ASEnvironmentState) {
-    .hierarchyState = ASEnvironmentHierarchyStateCreate(),
-    .layoutOptionsState = ASEnvironmentLayoutOptionsStateCreate()
+    .layoutOptionsState = _ASEnvironmentLayoutOptionsStateCreate(),
+    .hierarchyState = _ASEnvironmentHierarchyStateCreate()
   };
 }
\ No newline at end of file
diff --git a/AsyncDisplayKit/Layout/ASLayoutSpec.mm b/AsyncDisplayKit/Layout/ASLayoutSpec.mm
index 7c7598b90a..94e7e0a1a9 100644
--- a/AsyncDisplayKit/Layout/ASLayoutSpec.mm
+++ b/AsyncDisplayKit/Layout/ASLayoutSpec.mm
@@ -81,10 +81,8 @@ static NSString * const kDefaultChildrenKey = @"kDefaultChildrenKey";
 
     id<ASLayoutable> finalLayoutable = [child finalLayoutable];
     if (finalLayoutable != child) {
-      // Copy layout options
-      ASEnvironmentState environmentState = finalLayoutable.environmentState;
-      environmentState.layoutOptionsState = child.environmentState.layoutOptionsState;
-      finalLayoutable.environmentState = environmentState;
+      // Layout options state of child needs to be copied to final layoutable
+      finalLayoutable.environmentState.layoutOptionsState = child.environmentState.layoutOptionsState;
       return finalLayoutable;
     }
   }
@@ -159,6 +157,9 @@ static NSString * const kDefaultChildrenKey = @"kDefaultChildrenKey";
   _environmentState = environmentState;
 }
 
+// Subclasses can override this method to return NO, because upward propagation is not enabled if a layout
+// specification has more than one child. Currently ASStackLayoutSpec and ASStaticLayoutSpec are currently
+// the specifications that are known to have more than one.
 - (BOOL)supportsUpwardPropagation
 {
   return YES;
diff --git a/AsyncDisplayKit/Layout/ASLayoutableExtensibility.h b/AsyncDisplayKit/Layout/ASLayoutableExtensibility.h
index 1451368d27..c35d04f046 100644
--- a/AsyncDisplayKit/Layout/ASLayoutableExtensibility.h
+++ b/AsyncDisplayKit/Layout/ASLayoutableExtensibility.h
@@ -6,7 +6,7 @@
 //  Copyright © 2016 Facebook. All rights reserved.
 //
 
-#import <UIKit/UIKit.h>
+#import <UIKit/UIGeometry.h>
 
 @protocol ASLayoutableExtensibility <NSObject>
 
diff --git a/AsyncDisplayKit/Layout/ASLayoutablePrivate.h b/AsyncDisplayKit/Layout/ASLayoutablePrivate.h
index d18d0b7419..ce2de20f6d 100644
--- a/AsyncDisplayKit/Layout/ASLayoutablePrivate.h
+++ b/AsyncDisplayKit/Layout/ASLayoutablePrivate.h
@@ -231,30 +231,39 @@ extern void ASLayoutableClearCurrentContext();
 #define ASEnvironmentLayoutExtensibilityForwarding \
 - (void)setLayoutOptionExtensionBool:(BOOL)value atIndex:(int)idx\
 {\
+  _propertyLock.lock();\
   _ASEnvironmentLayoutOptionsExtensionSetBoolAtIndex(self, idx, value);\
+  _propertyLock.unlock();\
 }\
 \
 - (BOOL)layoutOptionExtensionBoolAtIndex:(int)idx\
 {\
+  ASDN::MutexLocker l(_propertyLock);\
   return _ASEnvironmentLayoutOptionsExtensionGetBoolAtIndex(self, idx);\
 }\
 \
 - (void)setLayoutOptionExtensionInteger:(NSInteger)value atIndex:(int)idx\
 {\
+  _propertyLock.lock();\
   _ASEnvironmentLayoutOptionsExtensionSetIntegerAtIndex(self, idx, value);\
+  _propertyLock.unlock();\
 }\
 \
 - (NSInteger)layoutOptionExtensionIntegerAtIndex:(int)idx\
 {\
+  ASDN::MutexLocker l(_propertyLock);\
   return _ASEnvironmentLayoutOptionsExtensionGetIntegerAtIndex(self, idx);\
 }\
 \
 - (void)setLayoutOptionExtensionEdgeInsets:(UIEdgeInsets)value atIndex:(int)idx\
 {\
+  _propertyLock.lock();\
   _ASEnvironmentLayoutOptionsExtensionSetEdgeInsetsAtIndex(self, idx, value);\
+  _propertyLock.unlock();\
 }\
 \
 - (UIEdgeInsets)layoutOptionExtensionEdgeInsetsAtIndex:(int)idx\
 {\
+  ASDN::MutexLocker l(_propertyLock);\
   return _ASEnvironmentLayoutOptionsExtensionGetEdgeInsetsAtIndex(self, idx);\
 }\