diff --git a/GraphicsMagick.spec b/GraphicsMagick.spec
index 1cf9524..8e8051a 100644
--- a/GraphicsMagick.spec
+++ b/GraphicsMagick.spec
@@ -16,12 +16,15 @@
 
 %define multilib_archs x86_64 %{ix86} ppc64 ppc s390x s390 sparc64 sparcv9
 # hack for older platforms/rpm-versions that do not support %%__isa_bits (like el5)
+%ifarch %{multilib_archs}
 %if ! 0%{?__isa_bits:1}
 %ifarch x86_64 s390x ia64 ppc64 sparc64
 %global __isa_bits 64
 %else
 %global __isa_bits 32
 %endif
+%endif
+%endif
 
 Summary: An ImageMagick fork, offering faster image generation and better quality
 Name: GraphicsMagick