diff --git a/lib/compiler/build_runner.zig b/lib/compiler/build_runner.zig
index 82d58e4592ac396bd1623f1b572d6706c46427d4..eed48e79adfa839ebdcd395c297ae1f47761c6a1 100644
--- a/lib/compiler/build_runner.zig
+++ b/lib/compiler/build_runner.zig
@@ -1410,12 +1410,13 @@ fn workerMakeOneStep(
     if (s.max_rss != 0) {
         var dispatch_deps: std.ArrayList(*Step) = .empty;
         defer dispatch_deps.deinit(gpa);
-        dispatch_deps.ensureUnusedCapacity(gpa, run.memory_blocked_steps.items.len) catch @panic("OOM");
 
         {
             run.max_rss_mutex.lockUncancelable(io);
             defer run.max_rss_mutex.unlock(io);
 
+            dispatch_deps.ensureUnusedCapacity(gpa, run.memory_blocked_steps.items.len) catch @panic("OOM");
+
             // Give the memory back to the scheduler.
             run.claimed_rss -= s.max_rss;
             // Avoid kicking off too many tasks that we already know will not have