diff --git a/complex.c b/complex.c
index 6b14ae6907..b65bc8a61c 100644
--- a/complex.c
+++ b/complex.c
@@ -2209,6 +2209,8 @@ Init_Complex(void)
      */
     rb_define_const(rb_cComplex, "I",
 		    f_complex_new_bang2(rb_cComplex, ZERO, ONE));
+
+    rb_provide("complex.so");	/* for backward compatibility */
 }
 
 /*
diff --git a/rational.c b/rational.c
index e50497944f..23b4bb0864 100644
--- a/rational.c
+++ b/rational.c
@@ -2614,6 +2614,8 @@ Init_Rational(void)
     rb_define_method(rb_cString, "to_r", string_to_r, 0);
 
     rb_define_private_method(CLASS_OF(rb_cRational), "convert", nurat_s_convert, -1);
+
+    rb_provide("rational.so");	/* for backward compatibility */
 }
 
 /*