diff --git a/src/net/tls/TLSSocket.cpp b/src/net/tls/TLSSocket.cpp
index 18bb7b9c..2eab2ad1 100644
--- a/src/net/tls/TLSSocket.cpp
+++ b/src/net/tls/TLSSocket.cpp
@@ -280,7 +280,7 @@ ssize_t TLSSocket::gnutlsPullFunc
 }
 
 
-ref <security::cert::certificateChain> TLSSocket::getPeerCertificates()
+ref <security::cert::certificateChain> TLSSocket::getPeerCertificates() const
 {
 	unsigned int certCount = 0;
 	const gnutls_datum* rawData = gnutls_certificate_get_peers
diff --git a/vmime/net/tls/TLSSocket.hpp b/vmime/net/tls/TLSSocket.hpp
index 8fb22990..5b2b7bb4 100644
--- a/vmime/net/tls/TLSSocket.hpp
+++ b/vmime/net/tls/TLSSocket.hpp
@@ -75,7 +75,7 @@ public:
 	  * @return server certificate chain, or NULL if the handshake
 	  * has not been performed yet
 	  */
-	ref <security::cert::certificateChain> getPeerCertificates();
+	ref <security::cert::certificateChain> getPeerCertificates() const;
 
 
 	// Implementation of 'socket'