diff --git a/configure b/configure
index 8bce35d713..5ac2a1495b 100755
--- a/configure
+++ b/configure
@@ -23683,7 +23683,7 @@ if test "x${PBX_UNBOUND}" != "x1" -a "${USE_UNBOUND}" != "no"; then
          pbxlibdir="-L${UNBOUND_DIR}"
       fi
    fi
-   pbxfuncname="ub_ctx_add_ta_autr"
+   pbxfuncname="ub_ctx_delete"
    if test "x${pbxfuncname}" = "x" ; then   # empty lib, assume only headers
       AST_UNBOUND_FOUND=yes
    else
@@ -23777,6 +23777,49 @@ fi
 
 
 
+    if test "x${PBX_UNBOUND_CONST_PARAMS}" != "x1" -a "${USE_UNBOUND_CONST_PARAMS}" != "no"; then
+        { $as_echo "$as_me:${as_lineno-$LINENO}: checking for UNBOUND_VERSION_MAJOR declared in unbound.h" >&5
+$as_echo_n "checking for UNBOUND_VERSION_MAJOR declared in unbound.h... " >&6; }
+        saved_cppflags="${CPPFLAGS}"
+        if test "x${UNBOUND_CONST_PARAMS_DIR}" != "x"; then
+            UNBOUND_CONST_PARAMS_INCLUDE="-I${UNBOUND_CONST_PARAMS_DIR}/include"
+        fi
+        CPPFLAGS="${CPPFLAGS} ${UNBOUND_CONST_PARAMS_INCLUDE}"
+
+        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+ #include <unbound.h>
+int
+main ()
+{
+#if !defined(UNBOUND_VERSION_MAJOR)
+                                    (void) UNBOUND_VERSION_MAJOR;
+                                #endif
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+     { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+                PBX_UNBOUND_CONST_PARAMS=1
+
+$as_echo "#define HAVE_UNBOUND_CONST_PARAMS 1" >>confdefs.h
+
+
+
+else
+     { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
+        CPPFLAGS="${saved_cppflags}"
+    fi
+
+
 
 if test "x${PBX_UNIXODBC}" != "x1" -a "${USE_UNIXODBC}" != "no"; then
    pbxlibdir=""
diff --git a/configure.ac b/configure.ac
index ed6f8a8d45..8ea1cb038d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2101,7 +2101,8 @@ AST_EXT_LIB_CHECK([NEWT], [newt], [newtBell], [newt.h])
 # script bug which does not find the ldns library.  The bug is fixed in
 # v1.4.22 but that version is not easily detectable.
 #
-AST_EXT_LIB_CHECK([UNBOUND], [unbound], [ub_ctx_add_ta_autr], [unbound.h], [])
+AST_EXT_LIB_CHECK([UNBOUND], [unbound], [ub_ctx_delete], [unbound.h], [])
+AST_C_DECLARE_CHECK([UNBOUND_CONST_PARAMS], [UNBOUND_VERSION_MAJOR], [unbound.h])
 
 AST_EXT_LIB_CHECK([UNIXODBC], [odbc], [SQLConnect], [sql.h], [])
 
diff --git a/include/asterisk/autoconfig.h.in b/include/asterisk/autoconfig.h.in
index b48257ec0a..bdd93bb64c 100644
--- a/include/asterisk/autoconfig.h.in
+++ b/include/asterisk/autoconfig.h.in
@@ -1108,6 +1108,9 @@
 /* Define to 1 if you have the unbound library. */
 #undef HAVE_UNBOUND
 
+/* Define if your system has UNBOUND_VERSION_MAJOR declared. */
+#undef HAVE_UNBOUND_CONST_PARAMS
+
 /* Define to 1 if you have the <unistd.h> header file. */
 #undef HAVE_UNISTD_H
 
diff --git a/res/res_resolver_unbound.c b/res/res_resolver_unbound.c
index 3eeb651697..40f3cfe4bf 100644
--- a/res/res_resolver_unbound.c
+++ b/res/res_resolver_unbound.c
@@ -79,6 +79,17 @@ ASTERISK_REGISTER_FILE()
 	</configInfo>
  ***/
 
+/*!
+ * Unbound versions <= 1.4.20 declare string function parameters as 'char *'
+ * but versions >= 1.4.21 declare them as 'const char *'.  Since CentOS6 is still
+ * at 1.4.20, we need to cast away the 'const' if we detect the earlier version.
+ */
+#ifdef HAVE_UNBOUND_CONST_PARAMS
+#define UNBOUND_CHAR const char
+#else
+#define UNBOUND_CHAR char
+#endif
+
 /*! \brief Structure for an unbound resolver */
 struct unbound_resolver {
 	/*! \brief Resolver context itself */
@@ -292,7 +303,7 @@ static int unbound_resolver_resolve(struct ast_dns_query *query)
 	data->resolver = ao2_bump(cfg->global->state->resolver);
 	ast_dns_resolver_set_data(query, data);
 
-	res = ub_resolve_async(data->resolver->context, ast_dns_query_get_name(query),
+	res = ub_resolve_async(data->resolver->context, (UNBOUND_CHAR *)ast_dns_query_get_name(query),
 		ast_dns_query_get_rr_type(query), ast_dns_query_get_rr_class(query),
 		ao2_bump(query), unbound_resolver_callback, &data->id);
 
@@ -404,7 +415,7 @@ static int unbound_config_preapply(struct unbound_config *cfg)
 	if (!strcmp(cfg->global->hosts, "system")) {
 		res = ub_ctx_hosts(cfg->global->state->resolver->context, NULL);
 	} else if (!ast_strlen_zero(cfg->global->hosts)) {
-		res = ub_ctx_hosts(cfg->global->state->resolver->context, cfg->global->hosts);
+		res = ub_ctx_hosts(cfg->global->state->resolver->context, (UNBOUND_CHAR *)cfg->global->hosts);
 	}
 
 	if (res) {
@@ -419,7 +430,7 @@ static int unbound_config_preapply(struct unbound_config *cfg)
 
 		it_nameservers = ao2_iterator_init(cfg->global->nameservers, 0);
 		while ((nameserver = ao2_iterator_next(&it_nameservers))) {
-			res = ub_ctx_set_fwd(cfg->global->state->resolver->context, nameserver);
+			res = ub_ctx_set_fwd(cfg->global->state->resolver->context, (UNBOUND_CHAR *)nameserver);
 
 			if (res) {
 				ast_log(LOG_ERROR, "Failed to add nameserver '%s' to unbound resolver: %s\n",
@@ -434,7 +445,7 @@ static int unbound_config_preapply(struct unbound_config *cfg)
 	if (!strcmp(cfg->global->resolv, "system")) {
 		res = ub_ctx_resolvconf(cfg->global->state->resolver->context, NULL);
 	} else if (!ast_strlen_zero(cfg->global->resolv)) {
-		res = ub_ctx_resolvconf(cfg->global->state->resolver->context, cfg->global->resolv);
+		res = ub_ctx_resolvconf(cfg->global->state->resolver->context, (UNBOUND_CHAR *)cfg->global->resolv);
 	}
 
 	if (res) {
@@ -444,7 +455,7 @@ static int unbound_config_preapply(struct unbound_config *cfg)
 	}
 
 	if (!ast_strlen_zero(cfg->global->ta_file)) {
-		res = ub_ctx_add_ta_file(cfg->global->state->resolver->context, cfg->global->ta_file);
+		res = ub_ctx_add_ta_file(cfg->global->state->resolver->context, (UNBOUND_CHAR *)cfg->global->ta_file);
 
 		if (res) {
 			ast_log(LOG_ERROR, "Failed to set trusted anchor file to '%s' in unbound resolver: %s\n",
@@ -740,13 +751,13 @@ static enum ast_test_result_state nominal_test(struct ast_test *test, resolve_fn
 	static const size_t V4_SIZE = sizeof(struct in_addr);
 	static const size_t V6_SIZE = sizeof(struct in6_addr);
 
-	static const char *DOMAIN1 = "goose.feathers";
-	static const char *DOMAIN2 = "duck.feathers";
+	static UNBOUND_CHAR *DOMAIN1 = "goose.feathers";
+	static UNBOUND_CHAR *DOMAIN2 = "duck.feathers";
 
-	static const char *ADDR1 = "127.0.0.2";
-	static const char *ADDR2 = "127.0.0.3";
-	static const char *ADDR3 = "::1";
-	static const char *ADDR4 = "127.0.0.4";
+	static UNBOUND_CHAR *ADDR1 = "127.0.0.2";
+	static UNBOUND_CHAR *ADDR2 = "127.0.0.3";
+	static UNBOUND_CHAR *ADDR3 = "::1";
+	static UNBOUND_CHAR *ADDR4 = "127.0.0.4";
 
 	char addr1_buf[V4_SIZE];
 	char addr2_buf[V4_SIZE];
@@ -786,7 +797,7 @@ static enum ast_test_result_state nominal_test(struct ast_test *test, resolve_fn
 	ub_ctx_zone_add(resolver->context, DOMAIN2, "static");
 
 	for (i = 0; i < ARRAY_LEN(records); ++i) {
-		ub_ctx_data_add(resolver->context, records[i].as_string);
+		ub_ctx_data_add(resolver->context, (UNBOUND_CHAR *)records[i].as_string);
 	}
 
 	for (i = 0; i < ARRAY_LEN(runs); ++i) {
@@ -808,7 +819,7 @@ static enum ast_test_result_state nominal_test(struct ast_test *test, resolve_fn
 
 cleanup:
 	for (i = 0; i < ARRAY_LEN(records); ++i) {
-		ub_ctx_data_remove(resolver->context, records[i].as_string);
+		ub_ctx_data_remove(resolver->context, (UNBOUND_CHAR *)records[i].as_string);
 	}
 	ub_ctx_zone_remove(resolver->context, DOMAIN1);
 	ub_ctx_zone_remove(resolver->context, DOMAIN2);
@@ -1012,10 +1023,10 @@ static enum ast_test_result_state off_nominal_test(struct ast_test *test,
 
 	static const size_t V4_SIZE = sizeof(struct in_addr);
 
-	static const char *DOMAIN1 = "goose.feathers";
-	static const char *DOMAIN2 = "duck.feathers";
+	static UNBOUND_CHAR *DOMAIN1 = "goose.feathers";
+	static UNBOUND_CHAR *DOMAIN2 = "duck.feathers";
 
-	static const char *ADDR1 = "127.0.0.2";
+	static UNBOUND_CHAR *ADDR1 = "127.0.0.2";
 
 	char addr1_buf[V4_SIZE];
 
@@ -1046,7 +1057,7 @@ static enum ast_test_result_state off_nominal_test(struct ast_test *test,
 	ub_ctx_zone_add(resolver->context, DOMAIN2, "static");
 
 	for (i = 0; i < ARRAY_LEN(records); ++i) {
-		ub_ctx_data_add(resolver->context, records[i].as_string);
+		ub_ctx_data_add(resolver->context, (UNBOUND_CHAR *)records[i].as_string);
 	}
 
 	for (i = 0; i < ARRAY_LEN(runs); ++i) {
@@ -1196,7 +1207,7 @@ AST_TEST_DEFINE(resolve_naptr)
 
 	const struct ast_dns_record *record;
 
-	static const char * DOMAIN1 = "goose.feathers";
+	static char * DOMAIN1 = "goose.feathers";
 	int i;
 	enum ast_test_result_state res = AST_TEST_PASS;
 
@@ -1234,7 +1245,7 @@ AST_TEST_DEFINE(resolve_naptr)
 	ub_ctx_zone_add(resolver->context, DOMAIN1, "static");
 
 	for (i = 0; i < ARRAY_LEN(records); ++i) {
-		ub_ctx_data_add(resolver->context, records[i].zone_entry);
+		ub_ctx_data_add(resolver->context, (UNBOUND_CHAR *)records[i].zone_entry);
 	}
 
 	if (ast_dns_resolve(DOMAIN1, ns_t_naptr, ns_c_in, &result)) {
@@ -1311,8 +1322,8 @@ AST_TEST_DEFINE(resolve_srv)
 	RAII_VAR(struct unbound_config *, cfg, NULL, ao2_cleanup);
 	RAII_VAR(struct ast_dns_result *, result, NULL, ast_dns_result_free);
 	const struct ast_dns_record *record;
-	static const char *DOMAIN1 = "taco.bananas";
-	static const char *DOMAIN1_SRV = "taco.bananas 12345 IN SRV 10 20 5060 sip.taco.bananas";
+	static UNBOUND_CHAR *DOMAIN1 = "taco.bananas";
+	static UNBOUND_CHAR *DOMAIN1_SRV = "taco.bananas 12345 IN SRV 10 20 5060 sip.taco.bananas";
 	enum ast_test_result_state res = AST_TEST_PASS;
 
 	switch (cmd) {