diff --git a/src/kiss/Helpers.hx b/src/kiss/Helpers.hx
index b3e862f..2d4de08 100644
--- a/src/kiss/Helpers.hx
+++ b/src/kiss/Helpers.hx
@@ -214,11 +214,17 @@ class Helpers {
         function makeSwitchPattern(patternExp:ReaderExp):Array<Expr> {
             return switch (patternExp.def) {
                 case CallExp({pos: _, def: Symbol("when")}, whenExps):
-                    patternExp.checkNumArgs(2, 2, "(when [guard] [pattern])");
+                    patternExp.checkNumArgs(2, 2, "(when <guard> <pattern>)");
                     if (guard != null)
-                        throw CompileError.fromExp(caseExp, "case pattern can only have one `when` guard");
+                        throw CompileError.fromExp(caseExp, "case pattern can only have one `when` or `unless` guard");
                     guard = macro Prelude.truthy(${k.convert(whenExps[0])});
                     makeSwitchPattern(whenExps[1]);
+                case CallExp({pos: _, def: Symbol("unless")}, whenExps):
+                    patternExp.checkNumArgs(2, 2, "(unless <guard> <pattern>)");
+                    if (guard != null)
+                        throw CompileError.fromExp(caseExp, "case pattern can only have one `when` or `unless` guard");
+                    guard = macro !Prelude.truthy(${k.convert(whenExps[0])});
+                    makeSwitchPattern(whenExps[1]);
                 case ListEatingExp(exps) if (exps.length == 0):
                     throw CompileError.fromExp(patternExp, "list-eating pattern should not be empty");
                 case ListEatingExp(exps):
diff --git a/src/test/cases/BasicTestCase.kiss b/src/test/cases/BasicTestCase.kiss
index 3ddcdd6..dc92e53 100644
--- a/src/test/cases/BasicTestCase.kiss
+++ b/src/test/cases/BasicTestCase.kiss
@@ -369,6 +369,10 @@
         ((when false (or 5 6)) (Assert.fail))
         ((when true (or 7 8 9)) (Assert.fail))
         (otherwise (Assert.pass)))
+    (case 5
+        ((unless true (or 5 6)) (Assert.fail))
+        ((unless false (or 7 8 9)) (Assert.fail))
+        (otherwise (Assert.pass)))
     // In Haxe,
     // `switch (Some(true)) { case Some(true | false): "a"; default: "b"; }`
     // returns "a", so nested use of `or` in case patterns should also be valid: