diff --git a/CHANGELOG.md b/CHANGELOG.md
index 124a099b..fdd134c5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,11 @@
 ArduinoJson: change log
 =======================
 
+HEAD
+----
+
+* Fixed exception when using Flash strings as object keys (issue #784)
+
 v6.2.2-beta
 -----------
 
diff --git a/src/ArduinoJson/Strings/FixedSizeFlashString.hpp b/src/ArduinoJson/Strings/FixedSizeFlashString.hpp
index 6c636264..893cace8 100644
--- a/src/ArduinoJson/Strings/FixedSizeFlashString.hpp
+++ b/src/ArduinoJson/Strings/FixedSizeFlashString.hpp
@@ -15,7 +15,7 @@ class FixedSizeFlashString {
   bool equals(const char* expected) const {
     const char* actual = reinterpret_cast<const char*>(_str);
     if (!actual || !expected) return actual == expected;
-    return strcmp_P(actual, expected) == 0;
+    return strncmp_P(expected, actual, _size) == 0;
   }
 
   bool is_null() const {
diff --git a/src/ArduinoJson/Strings/ZeroTerminatedFlashString.hpp b/src/ArduinoJson/Strings/ZeroTerminatedFlashString.hpp
index d86e14e9..5b101272 100644
--- a/src/ArduinoJson/Strings/ZeroTerminatedFlashString.hpp
+++ b/src/ArduinoJson/Strings/ZeroTerminatedFlashString.hpp
@@ -14,7 +14,7 @@ class ZeroTerminatedFlashString {
   bool equals(const char* expected) const {
     const char* actual = reinterpret_cast<const char*>(_str);
     if (!actual || !expected) return actual == expected;
-    return strcmp_P(actual, expected) == 0;
+    return strcmp_P(expected, actual) == 0;
   }
 
   bool is_null() const {