diff --git a/build.py b/build.py
index 6c048a89a..89e130083 100644
--- a/build.py
+++ b/build.py
@@ -460,7 +460,8 @@ class Ns3:
         dbg_env = env.Copy()
         dbg_env.Append(CFLAGS = debug_flags, 
                        CXXFLAGS = debug_flags,
-                       CPPDEFINES = ['NS3_DEBUG_ENABLE'])
+                       CPPDEFINES = ['NS3_DEBUG_ENABLE',
+                                     'NS3_ASSERT_ENABLE'])
         # debug static support
         variant.static = True
         variant.env = dbg_env
@@ -472,7 +473,8 @@ class Ns3:
         dbg_env = env.Copy()
         dbg_env.Append(CFLAGS=debug_flags, 
                        CXXFLAGS=debug_flags,
-                       CPPDEFINES = ['NS3_DEBUG_ENABLE'])
+                       CPPDEFINES = ['NS3_DEBUG_ENABLE',
+                                     'NS3_ASSERT_ENABLE'])
         # debug shared support
         variant.static = False
         variant.env = dbg_env