diff --git a/hphp/compiler/analysis/emitter.cpp b/hphp/compiler/analysis/emitter.cpp
index 60667a706..4eb343f2c 100644
--- a/hphp/compiler/analysis/emitter.cpp
+++ b/hphp/compiler/analysis/emitter.cpp
@@ -7480,6 +7480,15 @@ Unit* hphp_compiler_parse(const char* code, int codeLen, const MD5& md5,
     Repo::get().commitUnit(ue, unitOrigin);
     Unit* unit = ue->create();
     delete ue;
+    if (unit->sn() == -1) {
+      // the unit was not committed to the Repo, probably because
+      // another thread did it first. Try to use the winner.
+      Unit* u = Repo::get().loadUnit(filename ? filename : "", md5);
+      if (u != nullptr) {
+        delete unit;
+        return u;
+      }
+    }
     return unit;
   } catch (const std::exception&) {
     // extern "C" function should not be throwing exceptions...
diff --git a/hphp/hhvm/process_init.cpp b/hphp/hhvm/process_init.cpp
index 0311e78a1..2a50ea839 100644
--- a/hphp/hhvm/process_init.cpp
+++ b/hphp/hhvm/process_init.cpp
@@ -120,6 +120,10 @@ void ProcessInit() {
     Logger::Error("Unable to find/load systemlib.php");
     _exit(1);
   }
+  // Save this in case the debugger needs it. Once we know if this
+  // process does not have debugger support, we'll clear it.
+  SystemLib::s_source = slib;
+
   SystemLib::s_unit = compile_string(slib.c_str(), slib.size(),
                                      "systemlib.php");
   if (!hhas.empty()) {
diff --git a/hphp/runtime/base/program_functions.cpp b/hphp/runtime/base/program_functions.cpp
index b8ddc652d..b5efb0239 100644
--- a/hphp/runtime/base/program_functions.cpp
+++ b/hphp/runtime/base/program_functions.cpp
@@ -923,6 +923,9 @@ static int execute_program_impl(int argc, char **argv) {
 
   po.isTempFile = vm.count("temp-file");
 
+  // forget the source for systemlib.php unless we are debugging
+  if (po.mode != "debug") SystemLib::s_source = "";
+
   // we need to initialize pcre cache table very early
   pcre_init();
 
@@ -1104,6 +1107,9 @@ static int execute_program_impl(int argc, char **argv) {
             free(new_argv);
             prepare_args(new_argc, new_argv, *client_args, nullptr);
           }
+          // Systemlib.php is not loaded again, so we need this if we
+          // are to hit any breakpoints in systemlib.
+          phpSetBreakPoints(localProxy.get());
           restart = true;
         } catch (const Eval::DebuggerClientExitException &e) {
           execute_command_line_end(0, false, nullptr);
@@ -1207,7 +1213,6 @@ string get_systemlib(string* hhas) {
   std::unique_ptr<char[]> data(new char[desc.m_len]);
   ifs.read(data.get(), desc.m_len);
   string ret = systemlib_split(string(data.get(), desc.m_len), hhas);
-  if (RuntimeOption::EnableDebugger) SystemLib::s_source = ret;
   return ret;
 }
 
diff --git a/hphp/test/quick/debugger/config.hdf b/hphp/test/quick/debugger/config.hdf
index 19f64c452..528b95f2f 100644
--- a/hphp/test/quick/debugger/config.hdf
+++ b/hphp/test/quick/debugger/config.hdf
@@ -3,6 +3,9 @@ Eval {
   AllowHhas = true
   EnableHipHopSyntax = true
   EnableObjDestructCall = true
+  JitASize = 10485760 # 10 MB
+  JitAStubsSize = 10485760 # 10 MB
+  JitGlobalDataSize = 2097152 # 2 MB
   Debugger {
     EnableDebugger = true
     EnableDebuggerColor = false
@@ -11,8 +14,6 @@ Eval {
 }
 
 Repo {
-  Local.Mode = r-
-  Central.Path = /var/facebook/hhvm/cli_%{schema}.hhbc
   Eval.Mode = readonly
   Commit = true
   DebugInfo = true
@@ -39,3 +40,5 @@ ErrorHandling {
 ResourceLimit {
   SerializationSizeLimit=134217728
 }
+
+
diff --git a/hphp/test/quick/debugger/list.php.disabled b/hphp/test/quick/debugger/list.php
similarity index 64%
rename from hphp/test/quick/debugger/list.php.disabled
rename to hphp/test/quick/debugger/list.php
index 5c4673460..f8a8abbbf 100644
--- a/hphp/test/quick/debugger/list.php.disabled
+++ b/hphp/test/quick/debugger/list.php
@@ -1,2 +1,4 @@
 <?php
 $h = new SplMaxHeap();
+$h->insert(1);
+
diff --git a/hphp/test/quick/debugger/list.php.expectf b/hphp/test/quick/debugger/list.php.expectf
index 2a032b06c..eea1ac7eb 100644
--- a/hphp/test/quick/debugger/list.php.expectf
+++ b/hphp/test/quick/debugger/list.php.expectf
@@ -1,14 +1,10 @@
 Program %s/list.php loaded. Type '[r]un' or '[c]ontinue' to go.
-step
-Break on line 2 of %s/list.php
-   1 <?php
-   2 $h = new SplMaxHeap();
-   3 (END)
-
-step
-Break at SplHeap::__construct() on line %d of systemlib.php
- %d    */
- %d   public function __construct() {}
- %d 
+%Sbr SplMaxHeap::insert()
+Breakpoint 1 set upon entering SplMaxHeap::insert()
+run
+Breakpoint 1 reached at SplHeap::insert() on line %d of systemlib.php
+ %d   public function insert($value) {
+ %d     $this->checkNotCorrupted();
+ %d     $index = $this->lowestFreeIndex();
 
 quit
diff --git a/hphp/test/quick/debugger/list.php.in b/hphp/test/quick/debugger/list.php.in
index 243229139..791f1bf30 100644
--- a/hphp/test/quick/debugger/list.php.in
+++ b/hphp/test/quick/debugger/list.php.in
@@ -1,3 +1,3 @@
-step
-step
-quit
\ No newline at end of file
+br SplMaxHeap::insert()
+run
+quit