diff --git a/lib/pure/json.nim b/lib/pure/json.nim
index e881fbff7b..d91da35451 100644
--- a/lib/pure/json.nim
+++ b/lib/pure/json.nim
@@ -465,11 +465,12 @@ proc `==`*(a, b: JsonNode): bool {.noSideEffect.} =
       if a.fields.len != b.fields.len: return false
       for key, val in a.fields:
         if not b.fields.hasKey(key): return false
-        when defined(nimHasEffectsOf):
-          {.noSideEffect.}:
+        {.cast(raises: []).}:
+          when defined(nimHasEffectsOf):
+            {.noSideEffect.}:
+              if b.fields[key] != val: return false
+          else:
             if b.fields[key] != val: return false
-        else:
-          if b.fields[key] != val: return false
       result = true
 
 proc hash*(n: OrderedTable[string, JsonNode]): Hash {.noSideEffect.}