diff --git a/lib/parse/html.py b/lib/parse/html.py
index e13b79f64..7a20e6529 100644
--- a/lib/parse/html.py
+++ b/lib/parse/html.py
@@ -26,20 +26,23 @@ class htmlHandler(ContentHandler):
     def __init__(self, page):
         ContentHandler.__init__(self)
 
-        self.__dbms = None
-        self.__page = page
+        self._dbms = None
+        self._page = page
 
         self.dbms = None
 
+    def _markAsErrorPage(self):
+        threadData = getCurrentThreadData()
+        threadData.lastErrorPage = (threadData.lastRequestUID, self._page)
+
     def startElement(self, name, attrs):
         if name == "dbms":
-            self.__dbms = attrs.get("value")
+            self._dbms = attrs.get("value")
 
         elif name == "error":
-            if re.search(attrs.get("regexp"), self.__page, re.I):
-                self.dbms = self.__dbms
-                threadData = getCurrentThreadData()
-                threadData.lastErrorPage = (threadData.lastRequestUID, self.__page)
+            if re.search(attrs.get("regexp"), self._page, re.I):
+                self.dbms = self._dbms
+                self._markAsErrorPage()
 
 def htmlParser(page):
     """
@@ -59,4 +62,8 @@ def htmlParser(page):
     else:
         kb.lastParserStatus = None
 
+    # generic SQL warning/error messages
+    if re.search(r"SQL (warning|error|syntax)", page, re.I):
+        handler._markAsErrorPage()
+
     return handler.dbms
diff --git a/lib/request/comparison.py b/lib/request/comparison.py
index 1b373e72e..f06c55bb1 100644
--- a/lib/request/comparison.py
+++ b/lib/request/comparison.py
@@ -29,7 +29,8 @@ from lib.core.settings import UPPER_RATIO_BOUND
 from lib.core.threads import getCurrentThreadData
 
 def comparison(page, headers, code=None, getRatioValue=False, pageLength=None):
-    return _adjust(_comparison(page, headers, code, getRatioValue, pageLength), getRatioValue)
+    _ = _adjust(_comparison(page, headers, code, getRatioValue, pageLength), getRatioValue)
+    return _
 
 def _adjust(condition, getRatioValue):
     if not any([conf.string, conf.regexp, conf.code]):
@@ -37,7 +38,7 @@ def _adjust(condition, getRatioValue):
         # PAYLOAD.WHERE.NEGATIVE response is considered as True; in switch based approach negative logic is not
         # applied as that what is by user considered as True is that what is returned by the comparison mechanism
         # itself
-        retVal = not (condition or False) if kb.negativeLogic else condition
+        retVal = not condition if kb.negativeLogic and condition is not None else condition
     else:
         retVal = condition if not getRatioValue else (MAX_RATIO if condition else MIN_RATIO)
 
@@ -67,7 +68,7 @@ def _comparison(page, headers, code, getRatioValue, pageLength):
 
     if page:
         # In case of an DBMS error page return None
-        if not kb.negativeLogic and kb.errorIsNone and (wasLastRequestDBMSError() or wasLastRequestHTTPError()):
+        if kb.errorIsNone and (wasLastRequestDBMSError() or wasLastRequestHTTPError()):
             return None
 
         # Dynamic content lines to be excluded before comparison