diff --git a/fpga/include/villas/fpga/card.hpp b/fpga/include/villas/fpga/card.hpp
index 20c89876d..4d838559c 100644
--- a/fpga/include/villas/fpga/card.hpp
+++ b/fpga/include/villas/fpga/card.hpp
@@ -75,7 +75,7 @@ public:
 	bool reset() { return true; }
 	void dump()  { }
 
-	ip::IpCore* lookupIp(std::string name) const;
+	ip::IpCore* lookupIp(const std::string& name) const;
 
 	ip::IpCoreList ips;		///< IPs located on this FPGA card
 
diff --git a/fpga/lib/card.cpp b/fpga/lib/card.cpp
index da0e2d830..b15328566 100644
--- a/fpga/lib/card.cpp
+++ b/fpga/lib/card.cpp
@@ -132,7 +132,8 @@ fpga::PCIeCardFactory::create()
 
 
 ip::IpCore*
-PCIeCard::lookupIp(std::string name) const {
+PCIeCard::lookupIp(const std::string& name) const
+{
 	for(auto& ip : ips) {
 		if(*ip == name) {
 			return ip.get();