diff --git a/ReactCommon/fabric/core/propsConversions.h b/ReactCommon/fabric/core/propsConversions.h
index 548b88f3d..bf2f96f6c 100644
--- a/ReactCommon/fabric/core/propsConversions.h
+++ b/ReactCommon/fabric/core/propsConversions.h
@@ -17,7 +17,11 @@ namespace facebook {
 namespace react {
 
 inline void fromDynamic(const folly::dynamic &value, bool &result) { result = value.getBool(); }
-inline void fromDynamic(const folly::dynamic &value, int &result) { result = value.getInt(); }
+inline void fromDynamic(const folly::dynamic &value, int &result) {
+  // All numbers from JS are treated as double, and JS cannot represent int64 in practice.
+  // So this always converts the value to int64 instead.
+  result = value.asInt();
+}
 inline void fromDynamic(const folly::dynamic &value, std::string &result) { result = value.getString(); }
 
 template <typename T>
diff --git a/ReactCommon/fabric/view/conversions.h b/ReactCommon/fabric/view/conversions.h
index cec142a7b..66cb25da0 100644
--- a/ReactCommon/fabric/view/conversions.h
+++ b/ReactCommon/fabric/view/conversions.h
@@ -201,7 +201,7 @@ inline void fromDynamic(const folly::dynamic &value, YGValue &result) {
       return;
     } else {
       if (stringValue.back() == '%') {
-        result = { folly::to<float>(stringValue.substr(stringValue.length() - 1)), YGUnitPercent };
+        result = { folly::to<float>(stringValue.substr(0, stringValue.length() - 1)), YGUnitPercent };
         return;
       } else {
         result = { folly::to<float>(stringValue), YGUnitPoint };