diff --git a/spock-core/src/main/java/org/spockframework/compiler/AbstractDeepBlockRewriter.java b/spock-core/src/main/java/org/spockframework/compiler/AbstractDeepBlockRewriter.java
index f4129615f3..f1cc5f13a1 100644
--- a/spock-core/src/main/java/org/spockframework/compiler/AbstractDeepBlockRewriter.java
+++ b/spock-core/src/main/java/org/spockframework/compiler/AbstractDeepBlockRewriter.java
@@ -149,6 +149,12 @@ public final void visitClosureExpression(ClosureExpression expr) {
       currSpecialMethodCall = NoSpecialMethodCall.INSTANCE; // unrelated closure terminates currSpecialMethodCall scope
     }
     try {
+      Statement code = expr.getCode();
+      if (!(code instanceof BlockStatement)) {
+        BlockStatement block = new BlockStatement();
+        block.addStatement(code);
+        expr.setCode(block);
+      }
       doVisitClosureExpression(expr);
     } finally {
       currClosure = oldClosure;
diff --git a/spock-specs/src/test-groovy-ge-4.0/groovy/org/spockframework/smoke/condition/ConditionG4Spec.groovy b/spock-specs/src/test-groovy-ge-4.0/groovy/org/spockframework/smoke/condition/ConditionG4Spec.groovy
index b598d8a54e..71a228a4cc 100644
--- a/spock-specs/src/test-groovy-ge-4.0/groovy/org/spockframework/smoke/condition/ConditionG4Spec.groovy
+++ b/spock-specs/src/test-groovy-ge-4.0/groovy/org/spockframework/smoke/condition/ConditionG4Spec.groovy
@@ -13,4 +13,14 @@ class ConditionG4Spec extends Specification {
     (0..<5) == [0, 1, 2, 3, 4]
     (0<..<5) == [1, 2, 3, 4]
   }
+
+  @Issue("https://github.com/spockframework/spock/issues/1845")
+  def "explicit assert in switch expression"() {
+    expect:
+    def b = 3
+    !!switch (b) {
+      case 3 -> assert 1 == 1
+      default -> assert 1 == 1
+    }
+  }
 }