diff --git a/tools/gn/import_manager.cc b/tools/gn/import_manager.cc
index 01c88b5..0213c33 100644
--- a/tools/gn/import_manager.cc
+++ b/tools/gn/import_manager.cc
@@ -8,6 +8,7 @@
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scheduler.h"
 #include "tools/gn/scope_per_file_provider.h"
+#include "tools/gn/trace.h"
 
 namespace {
 
@@ -16,6 +17,8 @@
                                       const SourceFile& file,
                                       const ParseNode* node_for_err,
                                       Err* err) {
+  ScopedTrace load_trace(TraceItem::TRACE_IMPORT_LOAD, file.value());
+
   const ParseNode* node = g_scheduler->input_file_manager()->SyncLoadFile(
       node_for_err->GetRange(), settings->build_settings(), file, err);
   if (!node)
@@ -87,6 +90,7 @@
   // is already processing the import.
   const Scope* import_scope = nullptr;
   {
+    base::TimeTicks import_block_begin = base::TimeTicks::Now();
     base::AutoLock lock(import_info->load_lock);
 
     if (!import_info->scope) {
@@ -99,6 +103,21 @@
         *err = import_info->load_result;
         return false;
       }
+    } else {
+      // Add trace if this thread was blocked for a long period of time and did
+      // not load the import itself.
+      base::TimeTicks import_block_end = base::TimeTicks::Now();
+      constexpr auto kImportBlockTraceThreshold =
+          base::TimeDelta::FromMilliseconds(20);
+      if (TracingEnabled() &&
+          import_block_end - import_block_begin > kImportBlockTraceThreshold) {
+        auto import_block_trace =
+            new TraceItem(TraceItem::TRACE_IMPORT_BLOCK, file.value(),
+                          base::PlatformThread::CurrentId());
+        import_block_trace->set_begin(import_block_begin);
+        import_block_trace->set_end(import_block_end);
+        AddTrace(import_block_trace);
+      }
     }
 
     // Promote the now-read-only scope to outside the load lock.
diff --git a/tools/gn/trace.cc b/tools/gn/trace.cc
index 2a1b460..74a3e71 100644
--- a/tools/gn/trace.cc
+++ b/tools/gn/trace.cc
@@ -170,6 +170,10 @@
     trace_log = new TraceLog;
 }
 
+bool TracingEnabled() {
+  return !!trace_log;
+}
+
 void AddTrace(TraceItem* item) {
   trace_log->Add(item);
 }
@@ -203,6 +207,8 @@
       case TraceItem::TRACE_CHECK_HEADER:
         headers_checked++;
         break;
+      case TraceItem::TRACE_IMPORT_LOAD:
+      case TraceItem::TRACE_IMPORT_BLOCK:
       case TraceItem::TRACE_SETUP:
       case TraceItem::TRACE_FILE_LOAD:
       case TraceItem::TRACE_FILE_WRITE:
@@ -281,6 +287,12 @@
       case TraceItem::TRACE_FILE_WRITE:
         out << "\"file_write\"";
         break;
+      case TraceItem::TRACE_IMPORT_LOAD:
+        out << "\"import_load\"";
+        break;
+      case TraceItem::TRACE_IMPORT_BLOCK:
+        out << "\"import_block\"";
+        break;
       case TraceItem::TRACE_SCRIPT_EXECUTE:
         out << "\"script_exec\"";
         break;
diff --git a/tools/gn/trace.h b/tools/gn/trace.h
index de8ab09..d211641 100644
--- a/tools/gn/trace.h
+++ b/tools/gn/trace.h
@@ -26,10 +26,12 @@
     TRACE_FILE_PARSE,
     TRACE_FILE_EXECUTE,
     TRACE_FILE_WRITE,
+    TRACE_IMPORT_LOAD,
+    TRACE_IMPORT_BLOCK,
     TRACE_SCRIPT_EXECUTE,
     TRACE_DEFINE_TARGET,
     TRACE_ON_RESOLVED,
-    TRACE_CHECK_HEADER,  // One file.
+    TRACE_CHECK_HEADER,   // One file.
     TRACE_CHECK_HEADERS,  // All files.
   };
 
@@ -88,6 +90,9 @@
 // Call to turn tracing on. It's off by default.
 void EnableTracing();
 
+// Returns whether tracing is enabled.
+bool TracingEnabled();
+
 // Adds a trace event to the log. Takes ownership of the pointer.
 void AddTrace(TraceItem* item);