diff --git a/ChangeLog b/ChangeLog
index ec62a46..1b4b649 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2021-07-06  Omar Polo  <op@omarpolo.com>
+
+	* configure (guessing_cflags): try to preserve CFLAGS/LDFLAGS
+
 2021-07-02  Omar Polo  <op@omarpolo.com>
 
 	* sandbox.c (filter): seccomp filter reworked: now it should work on x86 and possibly other arches too!
diff --git a/configure b/configure
index b201655..2cfcff2 100755
--- a/configure
+++ b/configure
@@ -32,13 +32,25 @@ echo "file config.log: writing..."
 
 # --------
 # default settings: initialize all vars here such that nothing is
-# leaked from the environment except for CC and CFLAGS
+# leaked from the environment except for CC, CFLAGS and LDFLAGS
 
 CC=`printf "all:\\n\\t@echo \\\$(CC)\\n" | make ${MAKE_FLAGS} -sf -`
-CFLAGS=`printf "all:\\n\\t@echo \\\$(CFLAGS)\\n" | make ${MAKE_FLAGS} -sf -`
-CFLAGS="${CFLAGS} -g -W -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes"
-CFLAGS="${CFLAGS} -Wwrite-strings -Wno-unused-parameter"
-LDFLAGS="-ltls -levent"
+
+guessing_cflags=0
+if [ -z "${CFLAGS}" ]; then
+	guessing_cflags=1
+	CFLAGS=`printf "all:\\n\\t@echo \\\$(CFLAGS)\\n" | make ${MAKE_FLAGS} -sf -`
+	CFLAGS="${CFLAGS} -W -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes"
+	CFLAGS="${CFLAGS} -Wwrite-strings -Wno-unused-parameter"
+fi
+
+guessing_ldflags=0
+if [ -z "${LDFLAGS}" ]; then
+	guessing_ldflags=1
+	LDFLAGS=`printf "all:\\n\\t@echo \\\$(LDFLAGS)\\n" | make ${MAKE_FLAGS} -sf -`
+	LDFLAGS="-ltls -levent -lcrypto"
+fi
+
 LD_IMSG=
 STATIC=
 YACC=yacc
@@ -53,15 +65,28 @@ BINDIR=
 
 INSTALL="install"
 
+add_cflags() {
+	if [ $guessing_cflags = 1 ]; then
+		CFLAGS="${CFLAGS} $1"
+	fi
+}
+
+add_ldflags() {
+	if [ $guessing_ldflags = 1 ]; then
+		LDFLAGS="${LDFLAGS} $1"
+	fi
+}
+
 # try to auto detect CFLAGS and LDFLAGS
 if which pkg-config 2>/dev/null 1>&2; then
 	if pkg-config libtls; then
-		CFLAGS="${CFLAGS} $(pkg-config --cflags libtls)"
-		LDFLAGS="$(pkg-config --libs libtls)"
+		add_cflags "$(pkg-config --cflags libtls)"
+		add_ldflags "$(pkg-config --libs libtls)"
 	fi
+
 	if pkg-config openssl; then
-		CFLAGS="${CFLAGS} $(pkg-config --cflags openssl)"
-		LDFLAGS="${LDFLAGS} $(pkg-config --libs openssl)"
+		add_cflags "$(pkg-config --cflags openssl)"
+		add_ldflags "$(pkg-config --libs openssl)"
 	fi
 
 	case "$(uname)" in
@@ -70,8 +95,8 @@ if which pkg-config 2>/dev/null 1>&2; then
 			;;
 		*)
 			if pkg-config libevent; then
-				CFLAGS="${CFLAGS} $(pkg-config --cflags libevent)"
-				LDFLAGS="${LDFLAGS} $(pkg-config --libs libevent)"
+				add_cflags "$(pkg-config --cflags libevent)"
+				add_ldflags "$(pkg-config --libs libevent)"
 			fi
 			;;
 	esac