diff --git a/lib/core/target.py b/lib/core/target.py
index 6ed69acba..82570db34 100644
--- a/lib/core/target.py
+++ b/lib/core/target.py
@@ -115,6 +115,12 @@ def _setRequestParams():
             else:
                 kb.processUserMarks = not test or test[0] not in ("n", "N")
 
+                if kb.processUserMarks and "=%s" % CUSTOM_INJECTION_MARK_CHAR in conf.data:
+                    warnMsg = "it seems that you've provided empty parameter value(s) "
+                    warnMsg += "for testing. Please, always use only valid parameter values "
+                    warnMsg += "so sqlmap could be able to run properly"
+                    logger.warn(warnMsg)
+
         if not (kb.processUserMarks and CUSTOM_INJECTION_MARK_CHAR in conf.data):
             if re.search(JSON_RECOGNITION_REGEX, conf.data):
                 message = "JSON data found in %s data. " % conf.method
@@ -210,6 +216,12 @@ def _setRequestParams():
                 else:
                     kb.processUserMarks = not test or test[0] not in ("n", "N")
 
+                    if kb.processUserMarks and "=%s" % CUSTOM_INJECTION_MARK_CHAR in _:
+                        warnMsg = "it seems that you've provided empty parameter value(s) "
+                        warnMsg += "for testing. Please, always use only valid parameter values "
+                        warnMsg += "so sqlmap could be able to run properly"
+                        logger.warn(warnMsg)
+
             if not kb.processUserMarks:
                 if place == PLACE.URI:
                     query = urlparse.urlsplit(value).query