diff --git a/clients/drcachesim/tools/invariant_checker.cpp b/clients/drcachesim/tools/invariant_checker.cpp
index 7be742a8b9a..e433f29dcf2 100644
--- a/clients/drcachesim/tools/invariant_checker.cpp
+++ b/clients/drcachesim/tools/invariant_checker.cpp
@@ -102,6 +102,9 @@ invariant_checker_t::parallel_shard_memref(void *shard_data, const memref_t &mem
     ++shard->ref_count;
     if (shard->tid == -1 && memref.data.tid != 0)
         shard->tid = memref.data.tid;
+    // XXX i#5538: Have the infrastructure provide a common instr and record count.
+    if (type_is_instr(memref.instr.type))
+        ++shard->instr_count_;
 #ifdef UNIX
     if (has_annotations_) {
         // Check conditions specific to the signal_invariants app, where it
@@ -191,6 +194,18 @@ invariant_checker_t::parallel_shard_memref(void *shard_data, const memref_t &mem
         shard->found_page_size_marker_ = true;
     }
 
+    if (memref.marker.type == TRACE_TYPE_MARKER &&
+        memref.marker.marker_type == TRACE_MARKER_TYPE_CHUNK_INSTR_COUNT) {
+        shard->chunk_instr_count_ = memref.marker.marker_value;
+    }
+    if (memref.marker.type == TRACE_TYPE_MARKER &&
+        memref.marker.marker_type == TRACE_MARKER_TYPE_CHUNK_FOOTER) {
+        report_if_false(shard,
+                        shard->chunk_instr_count_ != 0 &&
+                            shard->instr_count_ % shard->chunk_instr_count_ == 0,
+                        "Chunk instruction counts are inconsistent");
+    }
+
     // Invariant: a function marker should not appear between an instruction and its
     // memrefs or in the middle of a block (we assume elision is turned off and so a
     // callee entry will always be the top of a block).  (We don't check for other types
diff --git a/clients/drcachesim/tools/invariant_checker.h b/clients/drcachesim/tools/invariant_checker.h
index 66d72d78324..ff58ba01ce9 100644
--- a/clients/drcachesim/tools/invariant_checker.h
+++ b/clients/drcachesim/tools/invariant_checker.h
@@ -104,6 +104,8 @@ class invariant_checker_t : public analysis_tool_t {
         offline_file_type_t file_type_ = OFFLINE_FILE_TYPE_DEFAULT;
         uintptr_t last_window_ = 0;
         bool window_transition_ = false;
+        uint64_t chunk_instr_count_ = 0;
+        uint64_t instr_count_ = 0;
     };
 
     // We provide this for subclasses to run these invariants with custom
diff --git a/clients/drcachesim/tracer/raw2trace.cpp b/clients/drcachesim/tracer/raw2trace.cpp
index 45dec6d4225..89470378567 100644
--- a/clients/drcachesim/tracer/raw2trace.cpp
+++ b/clients/drcachesim/tracer/raw2trace.cpp
@@ -1102,6 +1102,12 @@ raw2trace_t::append_delayed_branch(void *tls)
             return "Failed to write to output file";
     }
     tdata->delayed_branch.clear();
+    if (tdata->cur_chunk_instr_count >= chunk_instr_count_) {
+        DEBUG_ASSERT(tdata->cur_chunk_instr_count == chunk_instr_count_);
+        std::string error = open_new_chunk(tdata);
+        if (!error.empty())
+            return error;
+    }
     return "";
 }
 
@@ -1225,6 +1231,14 @@ raw2trace_t::write(void *tls, const trace_entry_t *start, const trace_entry_t *e
                                 reinterpret_cast<const char *>(end) -
                                     reinterpret_cast<const char *>(start)))
         return "Failed to write to output file";
+    // If we're at the end of a block (minus its delayed branch) we need
+    // to split now to avoid going too far by waiting for the next instr.
+    if (tdata->cur_chunk_instr_count >= chunk_instr_count_) {
+        DEBUG_ASSERT(tdata->cur_chunk_instr_count == chunk_instr_count_);
+        std::string error = open_new_chunk(tdata);
+        if (!error.empty())
+            return error;
+    }
     return "";
 }