diff --git a/siputils.py b/siputils.py
index e17518d..6abc6b1 100644
--- a/siputils.py
+++ b/siputils.py
@@ -856,6 +856,13 @@ class Makefile:
 
         cppflags = []
 
+        if getattr(sys, "pydebug", False):
+            cppflags.append("-DPy_DEBUG")
+
+        if hasattr(sys, "abiflags"):
+            if 'd' in sys.abiflags:
+                cppflags.append("-DPy_DEBUG")
+
         if not self._debug:
             cppflags.append("-DNDEBUG")