diff --git a/Makefile.rules b/Makefile.rules
index 6cc4bd3cf3b..48cb690be28 100644
--- a/Makefile.rules
+++ b/Makefile.rules
@@ -313,6 +313,13 @@ ifeq ($(ENABLE_OPTIMIZED),1)
   CXX.Flags += $(OPTIMIZE_OPTION) $(OmitFramePointer)
   C.Flags   += $(OPTIMIZE_OPTION) $(OmitFramePointer)
   LD.Flags  += $(OPTIMIZE_OPTION)
+  ifdef DEBUG_RUNTIME
+    BuildMode := $(BuildMode)+Debug
+    CXX.Flags += -g
+    C.Flags   += -g
+    LD.Flags  += -g
+    KEEP_SYMBOLS := 1
+  endif
 else
   BuildMode := Debug
   CXX.Flags += -g
diff --git a/docs/MakefileGuide.html b/docs/MakefileGuide.html
index f996144e145..8e552484abe 100644
--- a/docs/MakefileGuide.html
+++ b/docs/MakefileGuide.html
@@ -626,6 +626,11 @@
     <dd>If set to any value, causes a bitcode library (.bc) to be built.</dd>
     <dt><a name="CONFIG_FILES"><tt>CONFIG_FILES</tt></a></dt>
     <dd>Specifies a set of configuration files to be installed.</dd>
+    <dt><a name="DEBUG_RUNTIME"><tt>DEBUG_RUNTIME</tt></a></dt>
+    <dd>If set to any value, causes the build to include debugging
+    symbols even in optimized objects, libraries and executables. This
+    alters the flags specified to the compilers and linkers. Debugging
+    isn't fun in an optimized build, but it is possible.</dd>
     <dt><a name="DIRS"><tt>DIRS</tt></a></dt>
     <dd>Specifies a set of directories, usually children of the current
     directory, that should also be made using the same goal. These directories