diff --git a/acinclude.m4 b/acinclude.m4
new file mode 100644
index 0000000..cd33f21
--- /dev/null
+++ b/acinclude.m4
@@ -0,0 +1,190 @@
+AC_DEFUN([ACX_PTHREAD], [
+AC_REQUIRE([AC_CANONICAL_HOST])
+AC_LANG_SAVE
+AC_LANG_C
+acx_pthread_ok=no
+
+# We used to check for pthread.h first, but this fails if pthread.h
+# requires special compiler flags (e.g. on True64 or Sequent).
+# It gets checked for in the link test anyway.
+
+# First of all, check if the user has set any of the PTHREAD_LIBS,
+# etcetera environment variables, and if threads linking works using
+# them:
+if test x"$PTHREAD_LIBS$PTHREAD_CFLAGS" != x; then
+        save_CFLAGS="$CFLAGS"
+        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+        save_LIBS="$LIBS"
+        LIBS="$PTHREAD_LIBS $LIBS"
+        AC_MSG_CHECKING([for pthread_join in LIBS=$PTHREAD_LIBS with CFLAGS=$PTHREAD_CFLAGS])
+        AC_TRY_LINK_FUNC(pthread_join, acx_pthread_ok=yes)
+        AC_MSG_RESULT($acx_pthread_ok)
+        if test x"$acx_pthread_ok" = xno; then
+                PTHREAD_LIBS=""
+                PTHREAD_CFLAGS=""
+        fi
+        LIBS="$save_LIBS"
+        CFLAGS="$save_CFLAGS"
+fi
+
+# We must check for the threads library under a number of different
+# names; the ordering is very important because some systems
+# (e.g. DEC) have both -lpthread and -lpthreads, where one of the
+# libraries is broken (non-POSIX).
+
+# Create a list of thread flags to try.  Items starting with a "-" are
+# C compiler flags, and other items are library names, except for "none"
+# which indicates that we try without any flags at all, and "pthread-config"
+# which is a program returning the flags for the Pth emulation library.
+
+acx_pthread_flags="pthreads none -Kthread -kthread lthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config"
+
+# The ordering *is* (sometimes) important.  Some notes on the
+# individual items follow:
+
+# pthreads: AIX (must check this before -lpthread)
+# none: in case threads are in libc; should be tried before -Kthread and
+#       other compiler flags to prevent continual compiler warnings
+# -Kthread: Sequent (threads in libc, but -Kthread needed for pthread.h)
+# -kthread: FreeBSD kernel threads (preferred to -pthread since SMP-able)
+# lthread: LinuxThreads port on FreeBSD (also preferred to -pthread)
+# -pthread: Linux/gcc (kernel threads), BSD/gcc (userland threads)
+# -pthreads: Solaris/gcc
+# -mthreads: Mingw32/gcc, Lynx/gcc
+# -mt: Sun Workshop C (may only link SunOS threads [-lthread], but it
+#      doesn't hurt to check since this sometimes defines pthreads too;
+#      also defines -D_REENTRANT)
+#      ... -mt is also the pthreads flag for HP/aCC
+# pthread: Linux, etcetera
+# --thread-safe: KAI C++
+# pthread-config: use pthread-config program (for GNU Pth library)
+
+case "${host_cpu}-${host_os}" in
+        *solaris*)
+
+        # On Solaris (at least, for some versions), libc contains stubbed
+        # (non-functional) versions of the pthreads routines, so link-based
+        # tests will erroneously succeed.  (We need to link with -pthreads/-mt/
+        # -lpthread.)  (The stubs are missing pthread_cleanup_push, or rather
+        # a function called by this macro, so we could check for that, but
+        # who knows whether they'll stub that too in a future libc.)  So,
+        # we'll just look for -pthreads and -lpthread first:
+
+        acx_pthread_flags="-pthreads pthread -mt -pthread $acx_pthread_flags"
+        ;;
+esac
+
+if test x"$acx_pthread_ok" = xno; then
+for flag in $acx_pthread_flags; do
+
+        case $flag in
+                none)
+                AC_MSG_CHECKING([whether pthreads work without any flags])
+                ;;
+
+                -*)
+                AC_MSG_CHECKING([whether pthreads work with $flag])
+                PTHREAD_CFLAGS="$flag"
+                ;;
+
+                pthread-config)
+                AC_CHECK_PROG(acx_pthread_config, pthread-config, yes, no)
+                if test x"$acx_pthread_config" = xno; then continue; fi
+                PTHREAD_CFLAGS="`pthread-config --cflags`"
+                PTHREAD_LIBS="`pthread-config --ldflags` `pthread-config --libs`"
+                ;;
+
+                *)
+                AC_MSG_CHECKING([for the pthreads library -l$flag])
+                PTHREAD_LIBS="-l$flag"
+                ;;
+        esac
+
+        save_LIBS="$LIBS"
+        save_CFLAGS="$CFLAGS"
+        LIBS="$PTHREAD_LIBS $LIBS"
+        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+
+        # Check for various functions.  We must include pthread.h,
+        # since some functions may be macros.  (On the Sequent, we
+        # need a special flag -Kthread to make this header compile.)
+        # We check for pthread_join because it is in -lpthread on IRIX
+        # while pthread_create is in libc.  We check for pthread_attr_init
+        # due to DEC craziness with -lpthreads.  We check for
+        # pthread_cleanup_push because it is one of the few pthread
+        # functions on Solaris that doesn't have a non-functional libc stub.
+        # We try pthread_create on general principles.
+        AC_TRY_LINK([#include <pthread.h>],
+                    [pthread_t th; pthread_join(th, 0);
+                     pthread_attr_init(0); pthread_cleanup_push(0, 0);
+                     pthread_create(0,0,0,0); pthread_cleanup_pop(0); ],
+                    [acx_pthread_ok=yes])
+
+        LIBS="$save_LIBS"
+        CFLAGS="$save_CFLAGS"
+
+        AC_MSG_RESULT($acx_pthread_ok)
+        if test "x$acx_pthread_ok" = xyes; then
+                break;
+        fi
+
+        PTHREAD_LIBS=""
+        PTHREAD_CFLAGS=""
+done
+fi
+
+# Various other checks:
+if test "x$acx_pthread_ok" = xyes; then
+        save_LIBS="$LIBS"
+        LIBS="$PTHREAD_LIBS $LIBS"
+        save_CFLAGS="$CFLAGS"
+        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+
+        # Detect AIX lossage: JOINABLE attribute is called UNDETACHED.
+        AC_MSG_CHECKING([for joinable pthread attribute])
+        attr_name=unknown
+        for attr in PTHREAD_CREATE_JOINABLE PTHREAD_CREATE_UNDETACHED; do
+            AC_TRY_LINK([#include <pthread.h>], [int attr=$attr; return attr;],
+                        [attr_name=$attr; break])
+        done
+        AC_MSG_RESULT($attr_name)
+        if test "$attr_name" != PTHREAD_CREATE_JOINABLE; then
+            AC_DEFINE_UNQUOTED(PTHREAD_CREATE_JOINABLE, $attr_name,
+                               [Define to necessary symbol if this constant
+                                uses a non-standard name on your system.])
+        fi
+
+        AC_MSG_CHECKING([if more special flags are required for pthreads])
+        flag=no
+        case "${host_cpu}-${host_os}" in
+            *-aix* | *-freebsd* | *-darwin*) flag="-D_THREAD_SAFE";;
+            *solaris* | *-osf* | *-hpux*) flag="-D_REENTRANT";;
+        esac
+        AC_MSG_RESULT(${flag})
+        if test "x$flag" != xno; then
+            PTHREAD_CFLAGS="$flag $PTHREAD_CFLAGS"
+        fi
+
+        LIBS="$save_LIBS"
+        CFLAGS="$save_CFLAGS"
+
+        # More AIX lossage: must compile with cc_r
+        AC_CHECK_PROG(PTHREAD_CC, cc_r, cc_r, ${CC})
+else
+        PTHREAD_CC="$CC"
+fi
+
+AC_SUBST(PTHREAD_LIBS)
+AC_SUBST(PTHREAD_CFLAGS)
+AC_SUBST(PTHREAD_CC)
+
+# Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND:
+if test x"$acx_pthread_ok" = xyes; then
+        ifelse([$1],,AC_DEFINE(HAVE_PTHREAD,1,[Define if you have POSIX threads libraries and header files.]),[$1])
+        :
+else
+        acx_pthread_ok=no
+        $2
+fi
+AC_LANG_RESTORE
+])dnl ACX_PTHREAD
diff --git a/btpd/Makefile.am b/btpd/Makefile.am
index ca0a096..72ae36a 100644
--- a/btpd/Makefile.am
+++ b/btpd/Makefile.am
@@ -15,7 +15,9 @@ btpd_SOURCES=\
 	upload.c upload.h\
 	util.c
 
-btpd_LDADD=../misc/libmisc.a -levent -lcrypto -lm
+CC=@PTHREAD_CC@
+CFLAGS=@CFLAGS@ @PTHREAD_CFLAGS@ @curl_CFLAGS@
+
+btpd_LDADD=@PTHREAD_LIBS@ ../misc/libmisc.a -levent -lcrypto -lm
 btpd_CPPFLAGS=-I$(top_srcdir)/misc @event_CPPFLAGS@ @openssl_CPPFLAGS@
-btpd_CFLAGS=@CURL_CFLAGS@
-btpd_LDFLAGS=@event_LDFLAGS@ @openssl_LDFLAGS@ @CURL_LDFLAGS@
+btpd_LDFLAGS=@event_LDFLAGS@ @openssl_LDFLAGS@ @curl_LDFLAGS@
diff --git a/configure.ac b/configure.ac
index af85fe1..0f51bab 100644
--- a/configure.ac
+++ b/configure.ac
@@ -10,16 +10,18 @@ AC_PROG_RANLIB
 CFLAGS="$CFLAGS -std=c99"
 CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE=1 -D_FILE_OFFSET_BITS=64"
 
-AC_ARG_WITH(event,
-[  --with-event=dir        use libevent installed in dir],
+ACX_PTHREAD([], [echo Must have pthread support; exit 1])
+
+AC_ARG_WITH(libevent,
+[  --with-libevent=dir     use libevent installed in dir],
 [
         AC_SUBST(event_LDFLAGS,["-L${withval}/lib -Wl,-rpath=${withval}/lib"])
         AC_SUBST(event_CPPFLAGS,"-I${withval}/include")
 ],
 [])
 
-AC_ARG_WITH(ssl,
-[  --with-ssl=dir          use openssl installed in dir],
+AC_ARG_WITH(openssl,
+[  --with-openssl=dir      use openssl installed in dir],
 [
         AC_SUBST(openssl_LDFLAGS,["-L${withval}/lib -Wl,-rpath=${withval}/lib"])
         AC_SUBST(openssl_CPPFLAGS,"-I${withval}/include")
@@ -71,12 +73,12 @@ if test x$CURLCONF = x -o \! \( -r "$CURLCONF" -a -x "$CURLCONF" \); then
    echo Must have the curl-config script
    exit 1
 else
-   AC_SUBST(CURL_CFLAGS, `$CURLCONF --cflags`)
-   AC_SUBST(CURL_LDFLAGS, `$CURLCONF --libs`)
+   AC_SUBST(curl_CFLAGS, `$CURLCONF --cflags`)
+   AC_SUBST(curl_LDFLAGS, `$CURLCONF --libs`)
 fi
 
 old_LDFLAGS="$LDFLAGS"
-LDFLAGS="$LDFLAGS $CURL_LDFLAGS"
+LDFLAGS="$LDFLAGS $curl_LDFLAGS"
 AC_CHECK_LIB(curl, curl_easy_strerror, :, echo Must have recent curl; exit 1)
 LDFLAGS=$old_LDFLAGS