diff --git a/caps/nsJSPrincipals.cpp b/caps/nsJSPrincipals.cpp
index b3199c480b29..a5d91708c1ed 100644
--- a/caps/nsJSPrincipals.cpp
+++ b/caps/nsJSPrincipals.cpp
@@ -27,7 +27,7 @@ using namespace mozilla::ipc;
 
 NS_IMETHODIMP_(MozExternalRefCountType)
 nsJSPrincipals::AddRef() {
-  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(int32_t(refcount) >= 0, "illegal refcnt");
   nsrefcnt count = ++refcount;
   NS_LOG_ADDREF(this, count, "nsJSPrincipals", sizeof(*this));
@@ -36,7 +36,7 @@ nsJSPrincipals::AddRef() {
 
 NS_IMETHODIMP_(MozExternalRefCountType)
 nsJSPrincipals::Release() {
-  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_DIAGNOSTIC_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(0 != refcount, "dup release");
   nsrefcnt count = --refcount;
   NS_LOG_RELEASE(this, count, "nsJSPrincipals");