--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2011-10-09  Bruno Haible  <bruno@clisp.org>
 
+	isinf: Fix for platforms where 'long double' == 'double'.
+	* m4/isinf.m4 (gl_ISINFL_WORKS): Require gl_LONG_DOUBLE_VS_DOUBLE.
+	Don't blindly assume 80-bit 'long double'.
+
 	isfinite: Fix for platforms where 'long double' == 'double'.
 	* m4/isfinite.m4 (gl_ISFINITEL_WORKS): Require gl_LONG_DOUBLE_VS_DOUBLE.
 	Don't blindly assume 80-bit 'long double'.

--- a/m4/isinf.m4
+++ b/m4/isinf.m4
@@ -1,4 +1,4 @@
-# isinf.m4 serial 7
+# isinf.m4 serial 8
 dnl Copyright (C) 2007-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -43,6 +43,7 @@
 [
   AC_REQUIRE([AC_PROG_CC])
   AC_REQUIRE([gl_BIGENDIAN])
+  AC_REQUIRE([gl_LONG_DOUBLE_VS_DOUBLE])
   AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
   AC_CACHE_CHECK([whether isinf(long double) works], [gl_cv_func_isinfl_works],
     [
@@ -89,7 +90,7 @@
       result |= 2;
   }
 
-#if ((defined __ia64 && LDBL_MANT_DIG == 64) || (defined __x86_64__ || defined __amd64__) || (defined __i386 || defined __i386__ || defined _I386 || defined _M_IX86 || defined _X86_))
+#if ((defined __ia64 && LDBL_MANT_DIG == 64) || (defined __x86_64__ || defined __amd64__) || (defined __i386 || defined __i386__ || defined _I386 || defined _M_IX86 || defined _X86_)) && !HAVE_SAME_LONG_DOUBLE_AS_DOUBLE
 /* Representation of an 80-bit 'long double' as an initializer for a sequence
    of 'unsigned int' words.  */
 # ifdef WORDS_BIGENDIAN