diff --git a/build-aux/speedo.mk b/build-aux/speedo.mk
index d1f980037..fcb7b2785 100644
--- a/build-aux/speedo.mk
+++ b/build-aux/speedo.mk
@@ -1259,7 +1259,8 @@ installer: all w32_insthelpers $(w32src)/inst-options.ini $(bdir)/README.txt
            done; \
          fi \
         )
-	$(MAKENSIS) -V2 \
+	$(MAKENSIS) -V2 $$($(MAKENSIS) -version \
+                           | grep -q ^v3 && echo "-INPUTCHARSET CP1252 ") \
                     -DINST_DIR=$(idir) \
                     -DINST6_DIR=$(idir6) \
                     -DBUILD_DIR=$(bdir) \