diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index 9f28f2d..30f52a8 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -58,6 +58,7 @@
             "the VM service.");
 
 DECLARE_FLAG(bool, enable_interpreter);
+DECLARE_FLAG(bool, trace_deoptimization);
 DECLARE_FLAG(bool, warn_on_pause_with_no_debugger);
 
 #ifndef PRODUCT
@@ -1868,6 +1869,9 @@
 // We currently don't have this info so we deoptimize all functions.
 void Debugger::DeoptimizeWorld() {
   BackgroundCompiler::Stop(isolate_);
+  if (FLAG_trace_deoptimization) {
+    THR_Print("Deopt for debugger\n");
+  }
   DeoptimizeFunctionsOnStack();
   // Iterate over all classes, deoptimize functions.
   // TODO(hausner): Could possibly be combined with RemoveOptimizedCode()
diff --git a/runtime/vm/isolate_reload.cc b/runtime/vm/isolate_reload.cc
index 5f18023..4b784f1 100644
--- a/runtime/vm/isolate_reload.cc
+++ b/runtime/vm/isolate_reload.cc
@@ -53,6 +53,8 @@
             false,
             "Assert that an isolate has reloaded at least once.")
 
+DECLARE_FLAG(bool, trace_deoptimization);
+
 #define I (isolate())
 #define Z (thread->zone())
 
@@ -1951,6 +1953,9 @@
 void IsolateReloadContext::InvalidateWorld() {
   TIR_Print("---- INVALIDATING WORLD\n");
   ResetMegamorphicCaches();
+  if (FLAG_trace_deoptimization) {
+    THR_Print("Deopt for reload\n");
+  }
   DeoptimizeFunctionsOnStack();
   ResetUnoptimizedICsOnStack();
   MarkAllFunctionsForRecompilation();
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index baa77d1..54d9bd5 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -3098,8 +3098,12 @@
 void Class::DisableCHAOptimizedCode(const Class& subclass) {
   ASSERT(Thread::Current()->IsMutatorThread());
   CHACodeArray a(*this);
-  if (FLAG_trace_deoptimization && a.HasCodes() && !subclass.IsNull()) {
-    THR_Print("Adding subclass %s\n", subclass.ToCString());
+  if (FLAG_trace_deoptimization && a.HasCodes()) {
+    if (subclass.IsNull()) {
+      THR_Print("Deopt for CHA (all)\n");
+    } else {
+      THR_Print("Deopt for CHA (new subclass %s)\n", subclass.ToCString());
+    }
   }
   a.DisableCode();
 }
@@ -9007,6 +9011,9 @@
   ASSERT(Thread::Current()->IsMutatorThread());
   ASSERT(IsOriginal());
   FieldDependentArray a(*this);
+  if (FLAG_trace_deoptimization && a.HasCodes()) {
+    THR_Print("Deopt for field guard (field %s)\n", ToCString());
+  }
   a.DisableCode();
 }
 
@@ -12968,6 +12975,9 @@
 
 void LibraryPrefix::InvalidateDependentCode() const {
   PrefixDependentArray a(*this);
+  if (FLAG_trace_deoptimization && a.HasCodes()) {
+    THR_Print("Deopt for lazy load (prefix %s)\n", ToCString());
+  }
   a.DisableCode();
   set_is_loaded();
 }