Index: autoconf/configure.ac
===================================================================
--- autoconf/configure.ac
+++ autoconf/configure.ac
@@ -73,6 +73,11 @@
   fi
 fi
 
+dnl Quit if it is an in-source build
+if test ${srcdir} == "." ; then
+  AC_MSG_ERROR([In-source builds are discouraged. Configure from a separate build directory.])
+fi
+
 dnl Default to empty (i.e. assigning the null string to) CFLAGS and CXXFLAGS,
 dnl instead of the autoconf default (for example, '-g -O2' for CC=gcc).
 : ${CFLAGS=}
Index: configure
===================================================================
--- configure
+++ configure
@@ -1999,6 +1999,12 @@
   fi
 fi
 
+if test ${srcdir} == "." ; then
+  { { echo "$as_me:$LINENO: error: In-source builds are discouraged. Configure from a separate build directory." >&5
+echo "$as_me: error: In-source builds are discouraged. Configure from a separate build directory." >&2;}
+   { (exit 1); exit 1; }; }
+fi
+
 : ${CFLAGS=}
 : ${CXXFLAGS=}