diff --git a/server/modules/filter/masking/maskingfilter.cc b/server/modules/filter/masking/maskingfilter.cc
index 54dda8a8c..cd33cc8ae 100644
--- a/server/modules/filter/masking/maskingfilter.cc
+++ b/server/modules/filter/masking/maskingfilter.cc
@@ -185,6 +185,28 @@ MaskingFilter* MaskingFilter::create(const char* zName, MXS_CONFIG_PARAMETER* pP
     if (sRules.get())
     {
         pFilter = new MaskingFilter(config, sRules);
+
+        if (config.treat_string_arg_as_field())
+        {
+            MXS_NOTICE("The parameter 'treat_string_arg_as_field' is enabled for %s. "
+                       "As a consequence, the query classifier cache must be disabled.",
+                       zName);
+
+            QC_CACHE_PROPERTIES cache_properties;
+            qc_get_cache_properties(&cache_properties);
+
+            if (cache_properties.max_size != 0)
+            {
+                cache_properties.max_size = 0;
+                qc_set_cache_properties(&cache_properties);
+
+                MXS_NOTICE("Query classifier cache disabled.");
+            }
+            else
+            {
+                MXS_NOTICE("The query classifier cache was disabled already.");
+            }
+        }
     }
 
     return pFilter;