diff --git a/old-configure.in b/old-configure.in
index cd62962f5f..9248f461e9 100644
--- a/old-configure.in
+++ b/old-configure.in
@@ -195,11 +195,6 @@ case "$target" in
             MSVC_CMP_RUNTIME_DLL=vcomp140.dll
             MSVC_CXX_RUNTIME_DLL=msvcp140.dll
 
-            MOZ_CHECK_HEADER(dia2.h, MSVC_HAS_DIA_SDK=1)
-            if test -n "$MSVC_HAS_DIA_SDK"; then
-                AC_DEFINE(MSVC_HAS_DIA_SDK)
-            fi
-
             # C5026: move constructor was implicitly defined as deleted
             CXXFLAGS="$CXXFLAGS -wd5026"