diff --git a/ChangeLog.txt b/ChangeLog.txt
index ab0d7d0f..81504232 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -6,6 +6,7 @@ Broker:
   use. Closes #487178.
 - Fix detection of broken connections on Windows. Closes #485143.
 - Close stdin etc. when daemonised. Closes #485589.
+- Fix incorrect detection of FreeBSD and OpenBSD. Closes #485131.
 
 Client library:
 - mosq->want_write should be cleared immediately before a call to SSL_write,
diff --git a/config.mk b/config.mk
index 01532c3c..9eb5fe5c 100644
--- a/config.mk
+++ b/config.mk
@@ -115,7 +115,7 @@ LIB_LDFLAGS:=${LDFLAGS}
 BROKER_CFLAGS:=${LIB_CFLAGS} ${CPPFLAGS} -DVERSION="\"${VERSION}\"" -DTIMESTAMP="\"${TIMESTAMP}\"" -DWITH_BROKER
 CLIENT_CFLAGS:=${CFLAGS} ${CPPFLAGS} -I../lib -DVERSION="\"${VERSION}\""
 
-ifneq ($(or $(find $(UNAME),FreeBSD), $(find $(UNAME),OpenBSD)),)
+ifneq ($(or $(findstring $(UNAME),FreeBSD), $(findstring $(UNAME),OpenBSD)),)
 	BROKER_LIBS:=-lm
 else
 	BROKER_LIBS:=-ldl -lm