diff --git a/libsolidity/interface/CompilerStack.h b/libsolidity/interface/CompilerStack.h
index 74a7dfc57..57c761336 100644
--- a/libsolidity/interface/CompilerStack.h
+++ b/libsolidity/interface/CompilerStack.h
@@ -258,7 +258,7 @@ private:
 
 	ReadFileCallback m_readFile;
 	bool m_optimize = false;
-	size_t m_optimizeRuns = 200;
+	unsigned m_optimizeRuns = 200;
 	std::map<std::string, h160> m_libraries;
 	/// list of path prefix remappings, e.g. mylibrary: github.com/ethereum = /usr/local/ethereum
 	/// "context:prefix=target"
diff --git a/test/ExecutionFramework.h b/test/ExecutionFramework.h
index 1274d4006..f47f2743d 100644
--- a/test/ExecutionFramework.h
+++ b/test/ExecutionFramework.h
@@ -279,7 +279,7 @@ protected:
 		bytes data;
 	};
 
-	size_t m_optimizeRuns = 200;
+	unsigned m_optimizeRuns = 200;
 	bool m_optimize = false;
 	Address m_sender;
 	Address m_contractAddress;