diff --git a/CHANGELOG.md b/CHANGELOG.md
index a9ea5f4..1b3a2f0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@
 
 ### Changed
 - SC1090: A leading `$x/` or `$(x)/` is now treated as `./` when locating files
+- SC2154: Variables appearing in -z/-n tests are no longer considered unassigned
 
 
 ## v0.7.1 - 2020-04-04
diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index f5c1a18..9b92698 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -2231,6 +2231,12 @@ prop_checkUnassignedReferences40= verifyNotTree checkUnassignedReferences ": ${f
 prop_checkUnassignedReferences41= verifyNotTree checkUnassignedReferences "mapfile -t files 123; echo \"${files[@]}\""
 prop_checkUnassignedReferences42= verifyNotTree checkUnassignedReferences "mapfile files -t; echo \"${files[@]}\""
 prop_checkUnassignedReferences43= verifyNotTree checkUnassignedReferences "mapfile --future files; echo \"${files[@]}\""
+prop_checkUnassignedReferences_minusNPlain   = verifyNotTree checkUnassignedReferences "if [ -n \"$x\" ]; then echo $x; fi"
+prop_checkUnassignedReferences_minusZPlain   = verifyNotTree checkUnassignedReferences "if [ -z \"$x\" ]; then echo \"\"; fi"
+prop_checkUnassignedReferences_minusNBraced  = verifyNotTree checkUnassignedReferences "if [ -n \"${x}\" ]; then echo $x; fi"
+prop_checkUnassignedReferences_minusZBraced  = verifyNotTree checkUnassignedReferences "if [ -z \"${x}\" ]; then echo \"\"; fi"
+prop_checkUnassignedReferences_minusNDefault = verifyNotTree checkUnassignedReferences "if [ -n \"${x:-}\" ]; then echo $x; fi"
+prop_checkUnassignedReferences_minusZDefault = verifyNotTree checkUnassignedReferences "if [ -z \"${x:-}\" ]; then echo \"\"; fi"
 
 checkUnassignedReferences = checkUnassignedReferences' False
 checkUnassignedReferences' includeGlobals params t = warnings
diff --git a/src/ShellCheck/AnalyzerLib.hs b/src/ShellCheck/AnalyzerLib.hs
index 596340b..c9954d1 100644
--- a/src/ShellCheck/AnalyzerLib.hs
+++ b/src/ShellCheck/AnalyzerLib.hs
@@ -499,7 +499,11 @@ getModifiedVariables t =
             guard . not . null $ str
             return (t, token, str, DataString SourceChecked)
 
-        T_DollarBraced _ _ l -> do
+        TC_Unary _ _ "-n" token -> markAsChecked t token
+        TC_Unary _ _ "-z" token -> markAsChecked t token
+        TC_Nullary _ _ token -> markAsChecked t token
+
+        T_DollarBraced _ _ l -> maybeToList $ do
             let string = concat $ oversimplify l
             let modifier = getBracedModifier string
             guard $ any (`isPrefixOf` modifier) ["=", ":="]
@@ -516,6 +520,14 @@ getModifiedVariables t =
         T_ForIn id str words _ -> [(t, t, str, DataString $ SourceFrom words)]
         T_SelectIn id str words _ -> [(t, t, str, DataString $ SourceFrom words)]
         _ -> []
+  where
+    markAsChecked place token = mapMaybe (f place) $ getWordParts token
+    f place t = case t of
+            T_DollarBraced _ _ l ->
+                let str = getBracedReference $ concat $ oversimplify l in do
+                    guard $ isVariableName str
+                    return (place, t, str, DataString SourceChecked)
+            _ -> Nothing
 
 isClosingFileOp op =
     case op of