diff --git a/src/Package/Fetch.zig b/src/Package/Fetch.zig
index 1eebea4b89..00b1bd8f53 100644
--- a/src/Package/Fetch.zig
+++ b/src/Package/Fetch.zig
@@ -162,6 +162,7 @@ pub const JobQueue = struct {
         path: Cache.Path,
         manifest_ast: std.zig.Ast,
         manifest: Package.Manifest,
+        uses: usize,
 
         pub const Context = struct {
             pub fn hash(_: @This(), a: Fork) u32 {
@@ -575,6 +576,8 @@ pub fn run(f: *Fetch) RunError!void {
     if (remote.hash) |expected_hash| {
         const expected_project_id: Package.ProjectId = expected_hash.projectId();
         if (job_queue.fork_set.getKeyPtrAdapted(expected_project_id, @as(JobQueue.Fork.Adapter, .{}))) |fork| {
+            log.debug("using fork {f} for {s}", .{ fork.path, fork.manifest.name });
+            fork.uses += 1;
             f.package_root = fork.path;
             f.manifest_ast = fork.manifest_ast;
             f.manifest = fork.manifest;
diff --git a/src/main.zig b/src/main.zig
index 80921fc02f..ef5c9ec732 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -5213,6 +5213,7 @@ fn cmdBuild(gpa: Allocator, arena: Allocator, io: Io, args: []const []const u8,
                 .path = fork.path,
                 .manifest_ast = fork.manifest_ast,
                 .manifest = fork.manifest,
+                .uses = 0,
             }, {});
         }
     }
@@ -5279,6 +5280,7 @@ fn cmdBuild(gpa: Allocator, arena: Allocator, io: Io, args: []const []const u8,
                     .recursive = true,
                     .debug_hash = false,
                     .unlazy_set = unlazy_set,
+                    .fork_set = fork_set,
                     .mode = fetch_mode,
                     .prog_node = fetch_prog_node,
                 };
@@ -5344,6 +5346,26 @@ fn cmdBuild(gpa: Allocator, arena: Allocator, io: Io, args: []const []const u8,
                 job_queue.group.async(io, Package.Fetch.workerRun, .{ &fetch, "root" });
                 try job_queue.group.await(io);
 
+                {
+                    // Ensure that forks were actually used. This is done
+                    // before printing manifest errors because using a fork can
+                    // prevent them.
+                    var any_unused = false;
+                    for (fork_set.keys()) |*fork| {
+                        if (fork.uses == 0) {
+                            std.log.err("fork {f} matched no {s} packages", .{
+                                fork.path, fork.manifest.name,
+                            });
+                            any_unused = true;
+                        } else {
+                            std.log.info("fork {f} matched {d} {s} packages", .{
+                                fork.path, fork.uses, fork.manifest.name,
+                            });
+                        }
+                    }
+                    if (any_unused) process.exit(1);
+                }
+
                 try job_queue.consolidateErrors();
 
                 if (fetch.error_bundle.root_list.items.len > 0) {