diff --git a/include/villas/api.hpp b/include/villas/api.hpp
index df8881827..2b9cebfff 100644
--- a/include/villas/api.hpp
+++ b/include/villas/api.hpp
@@ -39,6 +39,8 @@ namespace villas {
 namespace node {
 namespace api {
 
+const int version = 1;
+
 /* Forward declarations */
 class Session;
 
diff --git a/lib/api/sessions/http.cpp b/lib/api/sessions/http.cpp
index 820689e2e..ba8d6e874 100644
--- a/lib/api/sessions/http.cpp
+++ b/lib/api/sessions/http.cpp
@@ -24,11 +24,13 @@
 
 #include <libwebsockets.h>
 
+#include <villas/exceptions.hpp>
 #include <villas/web.hpp>
 #include <villas/log.hpp>
 #include <villas/config.h>
 #include <villas/api/sessions/http.hpp>
 
+using namespace villas;
 using namespace villas::node;
 using namespace villas::node::api::sessions;
 
@@ -49,7 +51,8 @@ Http::Http(Api *a, lws *w) :
 	/* Parse request URI */
 	sscanf(uri, "/api/v%d", (int *) &version);
 
-	/** @todo Check version */
+	if (version != api::version)
+		throw RuntimeError("Unsupported API version: {}", version);
 
 	/* This is an OPTIONS request.
 	 *
diff --git a/lib/api/sessions/websocket.cpp b/lib/api/sessions/websocket.cpp
index 596cc9dce..0b58080c3 100644
--- a/lib/api/sessions/websocket.cpp
+++ b/lib/api/sessions/websocket.cpp
@@ -25,6 +25,7 @@
 #include <libwebsockets.h>
 
 #include <villas/web.hpp>
+#include <villas/exceptions.hpp>
 #include <villas/log.hpp>
 #include <villas/api/sessions/websocket.hpp>
 
@@ -41,7 +42,8 @@ WebSocket::WebSocket(Api *a, lws *w) :
 
 	sscanf(uri, "/v%d", (int *) &version);
 
-	/** @todo Check version */
+	if (version != api::version)
+		throw RuntimeError("Unsupported API version: {}", version);
 }
 
 WebSocket::~WebSocket()