diff --git a/SRC/configure.ac b/SRC/configure.ac
index 25599b6..76c5a0f 100644
--- a/SRC/configure.ac
+++ b/SRC/configure.ac
@@ -174,6 +174,10 @@ AC_CHECK_FUNCS(dlopen, ,
    [AC_CHECK_LIB(dl,dlopen, ,
        [AC_MSG_ERROR([echoping requires dlopen (dynamic loading of libraries) for plugins])])])
 
+dnl Checking size of ints, we often need it for binary protocols like ICP
+AC_CHECK_SIZEOF(int)
+AC_CHECK_SIZEOF(long)
+
 if test "$LIBIDN" = "1"; then
 CF_LIB_LIBIDN
 fi
diff --git a/SRC/icp.h b/SRC/icp.h
index bfdf726..9528459 100644
--- a/SRC/icp.h
+++ b/SRC/icp.h
@@ -11,10 +11,12 @@
 #define ICP_FLAG_HIT_OBJ	0x80000000ul
 #define ICP_FLAG_SRC_RTT	0x40000000ul
 
-#ifdef __alpha__
+#if SIZEOF_INT == 4
 typedef unsigned int u_num32;
-#else
+#elif SIZEOF_LONG == 4
 typedef unsigned long u_num32;
+#else
+#error "No suitable type for representing a 32-bits value"
 #endif
 
 struct icp_common_s {