diff --git a/compiler/guards.nim b/compiler/guards.nim
index 15922b3442..d51064ba8a 100644
--- a/compiler/guards.nim
+++ b/compiler/guards.nim
@@ -46,7 +46,7 @@ proc isLocation(n: PNode): bool = not n.isValue
 
 proc isLet(n: PNode): bool =
   if n.kind == nkSym:
-    if n.sym.kind in {skLet, skTemp, skForVar}:
+    if n.sym.kind in {skLet, skConst, skTemp, skForVar}: # guard immutable variables
       result = true
     elif n.sym.kind == skParam and skipTypes(n.sym.typ,
                                              abstractInst).kind notin {tyVar}:
diff --git a/tests/objvariant/tcorrectcheckedfield.nim b/tests/objvariant/tcorrectcheckedfield.nim
index e5e67c727d..acb3acda14 100644
--- a/tests/objvariant/tcorrectcheckedfield.nim
+++ b/tests/objvariant/tcorrectcheckedfield.nim
@@ -20,3 +20,25 @@ block: # issue #24021
       discard
     else:
       discard foo.z
+
+
+# bug #22791
+type Foo = object
+  case a: bool
+  of false:
+    discard
+  of true:
+    case b: bool
+    of false:
+      discard
+    of true:
+      c: bool
+
+const f = Foo(a: true, b: true, c: true)
+case f.a
+of true:
+  case f.b
+  of true:
+    echo f.c
+  else: discard
+else: discard
\ No newline at end of file