diff --git a/configure.in b/configure.in
index e05966e..a774691 100644
--- a/configure.in
+++ b/configure.in
@@ -1337,7 +1337,7 @@ packed_struct_unaligned=x
 if test "$rb_cv_packed_struct" != no; then
     AC_DEFINE_UNQUOTED([PACKED_STRUCT(x)], [$rb_cv_packed_struct])
     AS_CASE(["$target_cpu"],
-           [x86*|i?86|x64], [packed_struct_unaligned='PACKED_STRUCT(x)'])
+           [x86*|i?86|x64|powerpc64*|ppc64*], [packed_struct_unaligned='PACKED_STRUCT(x)'])
 else
     AC_DEFINE_UNQUOTED([PACKED_STRUCT(x)], x)
 fi