diff --git a/configure.in b/configure.in
index 37e9b3d23..056fb483f 100644
--- a/configure.in
+++ b/configure.in
@@ -505,7 +505,7 @@ AC_REPLACE_FUNCS(inet_aton putenv strerror memmove mkstemp)
 
 AC_CHECK_HEADERS(floatingpoint.h ieeefp.h nan.h)
 
-AC_CHECK_FUNCS(finite isinf isnan)
+AC_CHECK_FUNCS(finite isinf isnan copysign)
 
 # When testing for the presence of alloca, we need to add alloca.o
 # explicitly to LIBOBJS to make sure that it is translated to