diff --git a/Changes b/Changes
index 244f99fb6..f04fe554c 100644
--- a/Changes
+++ b/Changes
@@ -7,6 +7,8 @@ indicates the contributor was also the author of the fix; Thanks!
 
 **    Support interfaces and modports, bug102.  [Byron Bradley, Jeremy Bennett]
 
+***   Duplicate clock gate optimization on by default, bug621.
+
 ****  Fix arrayed input compile error, bug645. [Krzysztof Jankowski]
 
 ****  Fix GCC version runtime changes, bug651. [Jeremy Bennett]
diff --git a/src/V3Options.cpp b/src/V3Options.cpp
index 560be0e33..e901b7836 100644
--- a/src/V3Options.cpp
+++ b/src/V3Options.cpp
@@ -1307,7 +1307,7 @@ void V3Options::optimize(int level) {
     m_oSubst = flag;
     m_oSubstConst = flag;
     m_oTable = flag;
-    m_oDedupe = level >= 3;
+    m_oDedupe = flag;
     // And set specific optimization levels
     if (level >= 3) {
 	m_inlineMult = -1;	// Maximum inlining