--- a/toolkit/components/telemetry/TelemetryScalar.cpp
+++ b/toolkit/components/telemetry/TelemetryScalar.cpp
@@ -781,32 +781,32 @@ KeyedScalar::GetValue(nsTArray<KeyValueP
  */
 ScalarResult
 KeyedScalar::GetScalarForKey(const nsAString& aKey, ScalarBase** aRet)
 {
   if (aKey.IsEmpty()) {
     return ScalarResult::KeyIsEmpty;
   }
 
-  if (aKey.Length() >= kMaximumKeyStringLength) {
+  if (aKey.Length() > kMaximumKeyStringLength) {
     return ScalarResult::KeyTooLong;
   }
 
-  if (mScalarKeys.Count() >= kMaximumNumberOfKeys) {
-    return ScalarResult::TooManyKeys;
-  }
-
   NS_ConvertUTF16toUTF8 utf8Key(aKey);
 
   ScalarBase* scalar = nullptr;
   if (mScalarKeys.Get(utf8Key, &scalar)) {
     *aRet = scalar;
     return ScalarResult::Ok;
   }
 
+  if (mScalarKeys.Count() >= kMaximumNumberOfKeys) {
+    return ScalarResult::TooManyKeys;
+  }
+
   scalar = internal_ScalarAllocate(mScalarKind);
   if (!scalar) {
     return ScalarResult::InvalidType;
   }
 
   mScalarKeys.Put(utf8Key, scalar);
 
   *aRet = scalar;