diff --git a/mlir/lib/Pass/PassStatistics.cpp b/mlir/lib/Pass/PassStatistics.cpp
--- a/mlir/lib/Pass/PassStatistics.cpp
+++ b/mlir/lib/Pass/PassStatistics.cpp
@@ -226,10 +226,12 @@
     MutableArrayRef<OpPassManager> nestedPms = adaptor->getPassManagers();
 
     // Merge the statistics from the async pass managers into the main nested
-    // pass managers.
+    // pass managers.  Prepare recursively before merging.
     for (auto &asyncPM : adaptor->getParallelPassManagers()) {
-      for (unsigned i = 0, e = asyncPM.size(); i != e; ++i)
+      for (unsigned i = 0, e = asyncPM.size(); i != e; ++i) {
+        prepareStatistics(asyncPM[i]);
         asyncPM[i].mergeStatisticsInto(nestedPms[i]);
+      }
     }
 
     // Prepare the statistics of each of the nested passes.
diff --git a/mlir/test/Pass/pipeline-stats-nested.mlir b/mlir/test/Pass/pipeline-stats-nested.mlir
new file mode 100644
--- /dev/null
+++ b/mlir/test/Pass/pipeline-stats-nested.mlir
@@ -0,0 +1,24 @@
+// REQUIRES: asserts
+// Check that statistics in nested pipelines are not ignored and that this works with and without threading.
+// RUN: mlir-opt %s -verify-each=true -pass-pipeline='builtin.module(builtin.module(func.func(test-stats-pass,test-stats-pass)))' -mlir-pass-statistics -mlir-pass-statistics-display=list -mlir-disable-threading 2>&1 | FileCheck -check-prefix=LIST %s
+// RUN: mlir-opt %s -verify-each=true -pass-pipeline='builtin.module(builtin.module(func.func(test-stats-pass,test-stats-pass)))' -mlir-pass-statistics -mlir-pass-statistics-display=list                         2>&1 | FileCheck -check-prefix=LIST %s
+
+// RUN: mlir-opt %s -verify-each=true -pass-pipeline='builtin.module(builtin.module(func.func(test-stats-pass,test-stats-pass)))' -mlir-pass-statistics -mlir-pass-statistics-display=pipeline -mlir-disable-threading 2>&1 | FileCheck -check-prefix=PIPELINE %s
+// RUN: mlir-opt %s -verify-each=true -pass-pipeline='builtin.module(builtin.module(func.func(test-stats-pass,test-stats-pass)))' -mlir-pass-statistics -mlir-pass-statistics-display=pipeline                         2>&1 | FileCheck -check-prefix=PIPELINE %s
+
+// Check for the correct statistic values.
+// Each test-stats-pass will count two ops: the func.func and the func.return .
+//      LIST: (S) 4 num-ops
+// LIST-NEXT: (S) 4 num-ops2
+//      PIPELINE: (S) 2 num-ops
+// PIPELINE-NEXT: (S) 2 num-ops2
+//      PIPELINE: (S) 2 num-ops
+// PIPELINE-NEXT: (S) 2 num-ops2
+
+module {
+  module {
+    func.func @foo() {
+      return
+    }
+  }
+}