--- configure.ac.orig	2017-09-01 00:10:07 UTC
+++ configure.ac
@@ -72,7 +72,7 @@ AC_MSG_CHECKING(whether to compile debug
 AC_ARG_ENABLE(debug,
   [  --enable-debug = enable various debug output],
   [AC_SUBST( cppflag, [-D__RTMIDI_DEBUG__] ) AC_SUBST( cxxflag, [-g] ) AC_SUBST( object_path, [Debug] ) AC_MSG_RESULT(yes)],
-  [AC_SUBST( cppflag, [] ) AC_SUBST( cxxflag, [-O3] ) AC_SUBST( object_path, [Release] ) AC_MSG_RESULT(no)])
+  [AC_SUBST( cppflag, [] ) AC_SUBST( object_path, [Release] ) AC_MSG_RESULT(no)])
 
 # Set paths if prefix is defined
 if test "x$prefix" != "x" && test "x$prefix" != "xNONE"; then
@@ -85,7 +85,7 @@ CPPFLAGS="$CPPFLAGS $cppflag"
 
 # For debugging and optimization ... overwrite default because it has both -g and -O2
 #CXXFLAGS="$CXXFLAGS $cxxflag"
-CXXFLAGS="$cxxflag"
+CXXFLAGS+="$cxxflag"
 
 # Check compiler and use -Wall if gnu.
 if [test $GXX = "yes" ;] then
@@ -139,6 +139,11 @@ case $host in
   AC_CHECK_LIB(pthread, pthread_create, , AC_MSG_ERROR(RtMidi requires the pthread library!))
   ;;
 
+  *-*-freebsd*)
+  # Checks for pthread library.
+  AC_CHECK_LIB(pthread, pthread_create, , AC_MSG_ERROR(RtMidi requires the pthread library!))
+  ;;
+
   *-apple*)
   # Look for Core flag
   AC_ARG_WITH(core, [  --with-core = choose CoreMidi API support (mac only)])