diff --git a/CMakeLists.txt b/CMakeLists.txt
index 69e645389..e390192e4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -145,9 +145,9 @@ if (NOT OPENVAS_RUN_DIR)
   set (OPENVAS_RUN_DIR "/run/ospd")
 endif (NOT OPENVAS_RUN_DIR)
 
-if (NOT BUILD_WITH_NETSNMP)
+if (NOT DEFINED BUILD_WITH_NETSNMP)
   set (BUILD_WITH_NETSNMP TRUE)
-endif (NOT BUILD_WITH_NETSNMP)
+endif (NOT DEFINED BUILD_WITH_NETSNMP)
 
 set (OPENVAS_DATA_DIR    "${DATADIR}/openvas")
 set (OPENVAS_STATE_DIR   "${LOCALSTATEDIR}/lib/openvas")