diff --git a/include/pcp-cpp/pmda.hpp b/include/pcp-cpp/pmda.hpp
index 12c3bdf..e3d7565 100644
--- a/include/pcp-cpp/pmda.hpp
+++ b/include/pcp-cpp/pmda.hpp
@@ -1132,7 +1132,7 @@ class pmda {
 
                     validate_instance(description, id.instance);
 
-                    if (!description.flags & pcp::storable_metric) {
+                    if (!(description.flags & pcp::storable_metric)) {
                         // Metric does not support storing values.
                         throw pcp::exception(PM_ERR_PERMISSION);
                     }