diff --git a/lib/core/settings.py b/lib/core/settings.py
index 9960e4f29..c5e6da3f4 100644
--- a/lib/core/settings.py
+++ b/lib/core/settings.py
@@ -77,6 +77,9 @@ METADB_SUFFIX = "_masterdb"
 # minimum time response set needed for time-comparison based on standard deviation
 MIN_TIME_RESPONSES = 15
 
+# minimum comparison ratio set needed for searching valid union column number based on standard deviation
+MIN_UNION_RESPONSES = 5
+
 # after these number of blanks at the end inference should stop (just in case)
 INFERENCE_BLANK_BREAK = 15
 
diff --git a/lib/techniques/inband/union/test.py b/lib/techniques/inband/union/test.py
index e05365a4b..a0671b804 100644
--- a/lib/techniques/inband/union/test.py
+++ b/lib/techniques/inband/union/test.py
@@ -31,6 +31,7 @@ from lib.core.enums import DBMS
 from lib.core.enums import PAYLOAD
 from lib.core.settings import FROM_TABLE
 from lib.core.settings import UNION_STDEV_COEFF
+from lib.core.settings import MIN_UNION_RESPONSES
 from lib.core.unescaper import unescaper
 from lib.parse.html import htmlParser
 from lib.request.comparison import comparison
@@ -45,9 +46,13 @@ def __findUnionCharCount(comment, place, parameter, value, prefix, suffix, where
     pushValue(kb.errorIsNone)
     items, ratios = [], []
     kb.errorIsNone = False
+    lowerCount, upperCount = conf.uColsStart, conf.uColsStop
+
+    if abs(upperCount - lowerCount) < MIN_UNION_RESPONSES:
+        upperCount = lowerCount + MIN_UNION_RESPONSES
 
     min_, max_ = None, None
-    for count in range(conf.uColsStart, conf.uColsStop+1):
+    for count in range(lowerCount, upperCount+1):
         query = agent.forgeInbandQuery('', -1, count, comment, prefix, suffix, conf.uChar)
         payload = agent.payload(place=place, parameter=parameter, newValue=query, where=where)
         page, _ = Request.queryPage(payload, place=place, content=True, raise404=False)