diff --git a/internal/core/posts/service.go b/internal/core/posts/service.go
index e15652b..1bcb3f7 100644
--- a/internal/core/posts/service.go
+++ b/internal/core/posts/service.go
@@ -935,6 +935,11 @@ const (
 	maxTagLength = 640
 )
 
+// MaxContentLength is the post body cap, in BYTES — it matches the postv2
+// lexicon. Create and edit both enforce it through
+// normalizeAndValidatePostContent.
+const MaxContentLength = 500000
+
 // normalizeAndValidatePostContent is the definition of a well-formed Coves post,
 // and it is SHARED by the create and the edit path rather than duplicated across
 // them.
@@ -989,13 +994,12 @@ const (
 func normalizeAndValidatePostContent(post postContent) error {
 	// Global content limits (from lexicon)
 	const (
-		maxContentLength = 500000 // 500k bytes - matches the postv2 lexicon
-		maxTitleLength   = 3000   // 3k bytes
+		maxTitleLength = 3000 // 3k bytes
 	)
 
-	if post.Content != nil && len(*post.Content) > maxContentLength {
+	if post.Content != nil && len(*post.Content) > MaxContentLength {
 		return NewValidationError("content",
-			fmt.Sprintf("content too long (max %d characters)", maxContentLength))
+			fmt.Sprintf("content too long (max %d characters)", MaxContentLength))
 	}
 
 	if post.Title != nil && len(*post.Title) > maxTitleLength {
diff --git a/internal/core/posts/service_create_validation_test.go b/internal/core/posts/service_create_validation_test.go
index c7a9753..8cb0280 100644
--- a/internal/core/posts/service_create_validation_test.go
+++ b/internal/core/posts/service_create_validation_test.go
@@ -203,9 +203,10 @@ func TestService_CreateResolvesTheCommunityAndValidatesTheRequest(t *testing.T)
 	})
 
 	t.Run("Rejects content over the length limit", func(t *testing.T) {
-		// One byte past maxContentLength (500,000). The limit is what keeps a
-		// single record from being unbounded on the way to the PDS.
-		longContent := string(make([]byte, 500001))
+		// One byte past the service's own content cap, derived from it so a
+		// change to the cap cannot leave this fixture behind. The limit is what
+		// keeps a single record from being unbounded on the way to the PDS.
+		longContent := string(make([]byte, posts.MaxContentLength+1))
 		err := createPost(posts.CreatePostRequest{
 			Community: community.DID,
 			Content:   &longContent,
diff --git a/internal/core/posts/service_update_validation_test.go b/internal/core/posts/service_update_validation_test.go
index 44bcb9a..06f0f6f 100644
--- a/internal/core/posts/service_update_validation_test.go
+++ b/internal/core/posts/service_update_validation_test.go
@@ -125,7 +125,7 @@ func TestService_UpdateRefusesContentCreateWouldHaveRefused(t *testing.T) {
 		},
 		{
 			name: "content past the lexicon's cap",
-			req:  posts.UpdatePostRequest{Content: ptr(strings.Repeat("b", 500001))},
+			req:  posts.UpdatePostRequest{Content: ptr(strings.Repeat("b", posts.MaxContentLength+1))},
 		},
 		{
 			name: "a label outside the allowlist",