diff --git a/src/compiler.ts b/src/compiler.ts
index e035cab8ca..a4e33bf342 100644
--- a/src/compiler.ts
+++ b/src/compiler.ts
@@ -10067,7 +10067,11 @@ export class Compiler extends DiagnosticEmitter {
 
   /** Evaluates a boolean condition, determining whether it is TRUE, FALSE or UNKNOWN. */
   evaluateCondition(expr: ExpressionRef): ConditionKind {
-    assert(getExpressionType(expr) == TypeRef.I32);
+    let type = getExpressionType(expr);
+    if (type == TypeRef.Unreachable)
+      return ConditionKind.UNKNOWN;
+
+    assert(type == TypeRef.I32);
     var module = this.module;
     var evaled = module.runExpression(expr, ExpressionRunnerFlags.Default);
     if (evaled) {
diff --git a/tests/compiler/unknown-bool-ident.json b/tests/compiler/unknown-bool-ident.json
new file mode 100644
index 0000000000..9808373e96
--- /dev/null
+++ b/tests/compiler/unknown-bool-ident.json
@@ -0,0 +1,8 @@
+{
+  "asc_flags": [
+  ],
+  "stderr": [
+    "TS2304: Cannot find name 'unknown_var'.",
+    "EOF"
+  ]
+}
diff --git a/tests/compiler/unknown-bool-ident.ts b/tests/compiler/unknown-bool-ident.ts
new file mode 100644
index 0000000000..2b6c3b4f05
--- /dev/null
+++ b/tests/compiler/unknown-bool-ident.ts
@@ -0,0 +1,2 @@
+if (1 <= unknown_var) {}
+ERROR("EOF");
\ No newline at end of file
diff --git a/tests/compiler/unknown-bool-ident.untouched.wat b/tests/compiler/unknown-bool-ident.untouched.wat
new file mode 100644
index 0000000000..e69de29bb2