diff --git a/ChangeLog b/ChangeLog
index fd92d71fd1..6d93eef1cc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -5,6 +5,9 @@ Changes in version 0.2.0.19-alpha - 2008-0?-??
       recognize them.  Fixes bug 571.  Bugfix on 0.2.0.x.
     - Stop recommending that every server operator send mail to tor-ops.
       Resolves bug 597.  Bugfix on 0.1.2.x.
+    - Detect version of OSX where malloc_good_size is present in the
+      library but never actually declared.  Resolves bug 587.  Bugfix
+      on 0.2.0.x.
 
 
 Changes in version 0.2.0.18-alpha - 2008-01-25
diff --git a/acinclude.m4 b/acinclude.m4
index 7f27afd5a3..fb2eba834d 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -193,3 +193,17 @@ CPPFLAGS="$tor_saved_CPPFLAGS"
 
 ]) dnl end defun
 
+dnl Check whether the prototype for a function is present or missing.
+dnl Apple has a nasty habit of putting functions in their libraries (so that
+dnl AC_CHECK_FUNCS passes) but not actually declaring them in the headers.
+dnl
+dnl TOR_CHECK_PROTYPE(1:functionname, 2:macroname, 2: includes)
+AC_DEFUN([TOR_CHECK_PROTOTYPE], [
+ AC_CACHE_CHECK([for declaration of $1], tor_cv_$1_declared, [
+   AC_COMPILE_IFELSE(AC_LANG_PROGRAM([$3],[void *ptr= $1 ;]),
+                     tor_cv_$1_declared=yes,tor_cv_$1_declared=no)])
+if test x$tor_cv_$1_declared != xno ; then
+  AC_DEFINE($2, 1,
+       [Defined if the prototype for $1 seems to be present.])
+fi
+])
\ No newline at end of file
diff --git a/configure.in b/configure.in
index c7580eafa3..8e675a6d3f 100644
--- a/configure.in
+++ b/configure.in
@@ -275,6 +275,14 @@ dnl These headers are not essential
 
 AC_CHECK_HEADERS(stdint.h sys/types.h inttypes.h sys/param.h sys/wait.h limits.h sys/limits.h netinet/in.h arpa/inet.h machine/limits.h syslog.h sys/time.h sys/resource.h inttypes.h utime.h sys/utime.h sys/mman.h netintet/in.h netinet/in6.h malloc.h sys/syslimits.h malloc/malloc.h)
 
+TOR_CHECK_PROTOTYPE(malloc_good_size, HAVE_MALLOC_GOOD_SIZE_PROTOTYPE,
+[#ifdef HAVE_MALLOC_H
+#include <malloc.h>
+#endif
+#ifdef HAVE_MALLOC_MALLOC_H
+#include <malloc/malloc.h>
+#endif])
+
 AC_CHECK_HEADERS(net/if.h, net_if_found=1, net_if_found=0,
 [#ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>
diff --git a/src/common/util.c b/src/common/util.c
index 8f08c9b6af..0623093e64 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -224,6 +224,14 @@ _tor_free(void *mem)
   tor_free(mem);
 }
 
+#if defined(HAVE_MALLOC_GOOD_SIZE) && !defined(HAVE_MALLOC_GOOD_SIZE_PROTOTYPE)
+/* Some version of Mac OSX have malloc_good_size in their libc, but not
+ * actually defined in malloc/malloc.h.  We detect this and work around it by
+ * prototyping.
+ */
+extern size_t malloc_good_size(size_t size);
+#endif
+
 /** Allocate and return a chunk of memory of size at least *<b>size</p>, using
  * the same resources we would use to malloc *<b>sizep</b>.  Set *<b>sizep</b>
  * to the number of usable bytes in the chunk of memory. */