diff --git a/spec/antigenic.xml b/spec/antigenic.xml
index b8e0ff6..ee879f6 100644
--- a/spec/antigenic.xml
+++ b/spec/antigenic.xml
@@ -269,7 +269,7 @@
 		</upDownOperator>						
 	</operators>
 
-	<mcmc id="mcmc" chainLength="5000000" autoOptimize="true" operatorAnalysis="antigenic.ops">
+	<mcmc id="mcmc" chainLength="10000000" autoOptimize="true" operatorAnalysis="antigenic.ops">
 		<posterior id="posterior">
 			<prior id="prior">
 				
diff --git a/spec/antigenic_simple.xml b/spec/antigenic_simple.xml
index 65cb499..0acf35b 100644
--- a/spec/antigenic_simple.xml
+++ b/spec/antigenic_simple.xml
@@ -115,7 +115,7 @@
 		</upDownOperator>						
 	</operators>
 
-	<mcmc id="mcmc" chainLength="5000000" autoOptimize="true" operatorAnalysis="antigenic_simple.ops">
+	<mcmc id="mcmc" chainLength="10000000" autoOptimize="true" operatorAnalysis="antigenic_simple.ops">
 		<posterior id="posterior">
 			<prior id="prior">