diff --git a/modules/dtls_gw/rtpp_dtls_conn.c b/modules/dtls_gw/rtpp_dtls_conn.c
index 52400ca63..75d4eb65c 100644
--- a/modules/dtls_gw/rtpp_dtls_conn.c
+++ b/modules/dtls_gw/rtpp_dtls_conn.c
@@ -472,6 +472,11 @@ rtpp_dtls_conn_dtls_recv(struct rtpp_dtls_conn *self,
 #define SRTCP_PROTECT(a, b, c) srtp_protect_rtcp(a, b, c)
 #endif
 
+/* libsrtp2 < 2.6.0 only documents it as SRTP_MAX_TRAILER_LEN+4 */
+#if !defined(SRTP_MAX_SRTCP_TRAILER_LEN)
+#define SRTP_MAX_SRTCP_TRAILER_LEN (SRTP_MAX_TRAILER_LEN + 4)
+#endif
+
 static struct res_loc
 rtpp_dtls_conn_rtp_send(struct rtpp_dtls_conn *self, struct pkt_proc_ctx *pktxp)
 {
@@ -489,6 +494,15 @@ rtpp_dtls_conn_rtp_send(struct rtpp_dtls_conn *self, struct pkt_proc_ctx *pktxp)
         return (RES_HERE(-1));
     }
 
+    /*
+     * srtp_protect() and srtp_protect_rtcp() append the trailer in place,
+     * make sure it fits in data.buf (the SRTCP one is the larger of the two).
+     */
+    if (pktxp->pktp->size > sizeof(pktxp->pktp->data.buf) -
+      SRTP_MAX_SRTCP_TRAILER_LEN) {
+        return (RES_HERE(-1));
+    }
+
     if (pktxp->flags & PPROC_FLAG_COW) {
         struct rtp_packet *p = rtp_packet_alloc();
         if (p == NULL)
diff --git a/tests/dtls_gw/basic b/tests/dtls_gw/basic
index fc65adfea..bfc04242c 100755
--- a/tests/dtls_gw/basic
+++ b/tests/dtls_gw/basic
@@ -14,7 +14,7 @@ rm -f dtls_gw.?.rlog
  -D DSO="${TOP_BUILDDIR}/modules/dtls_gw/.libs/rtpp_dtls_gw_debug.so" \
  -D RECORD_DIR="${RECORD_DIR}" -D RECORD_SPL_DIR="${RECORD_SPL_DIR}" \
  -D SCENARIO="${RPTL_DIR}/examples/dtls.scenario.rptl" \
- -D PROMPT_NAME="${BUILDDIR}/dtls_gw.prompt" \
+ -D PROMPT_NAME="${BUILDDIR}/dtls_gw.prompt" -D PYINT="${PYINT}" \
  2>&1 > dtls_gw.vars
   echo ${?} > dtls_gw.rptl.rc
 } | tee dtls_gw.rlog
diff --git a/tests/dtls_gw/basic.rptl b/tests/dtls_gw/basic.rptl
index a1778ad3a..d72ea72fa 100644
--- a/tests/dtls_gw/basic.rptl
+++ b/tests/dtls_gw/basic.rptl
@@ -13,6 +13,7 @@ socket fwd: stdio: %%RTPPROXY_ARGS%% -i -> dtls_gw.f.creplies
 socket geno: stdio: %%RTPPROXY_ARGS%% -P -r %%RECORD_DIR%% -S %%RECORD_SPL_DIR%% -> dtls_gw.o.creplies
 .echo: OK: rtpproxy GenO started
 .include: %%SCENARIO%%
+.include: oversize.rptl
 .close: geno
 .echo: OK: wait for rtpproxy GenO shutdown
 .close: fwd
diff --git a/tests/dtls_gw/oversize.check.rptl b/tests/dtls_gw/oversize.check.rptl
new file mode 100644
index 000000000..d290c012f
--- /dev/null
+++ b/tests/dtls_gw/oversize.check.rptl
@@ -0,0 +1,2 @@
+fwd: Qv %%OS_CALLID%% from_tag_1 to_tag_1 npkts_ina nrelayed ndropped -> OS_STATS
+.eval: %%OS_STATS%% -> str_equal(OS_EXPECTED, OS_DONE)
diff --git a/tests/dtls_gw/oversize.rptl b/tests/dtls_gw/oversize.rptl
new file mode 100644
index 000000000..b3a018acb
--- /dev/null
+++ b/tests/dtls_gw/oversize.rptl
@@ -0,0 +1,16 @@
+# A plain RTP datagram that fills the whole receive buffer leaves no room
+# for the SRTP trailer: Fwd has to drop it instead of protecting it in place.
+.eval: dtls_gw_oversize -> OS_CALLID
+fwd: U %%OS_CALLID%% 0.0.0.0 0 from_tag_1 && M4:1 S -> str_split(&&, OS_PORT1, DTLS_PARAMS)
+.eval: %%DTLS_PARAMS%% -> str_split( , DTLS_MODE, DTLS_DIGALG, DTLS_DIGSUM)
+geno: U %%OS_CALLID%% 127.0.0.1 %%OS_PORT1%% from_tag_1 && M4:1 A %%DTLS_DIGALG%% %%DTLS_DIGSUM%% -> validate_port(_)
+geno: L %%OS_CALLID%% 0.0.0.0 0 from_tag_1 to_tag_1 && M4:1 S -> str_split(&&, OS_PORTO, DTLS_PARAMS)
+.eval: %%DTLS_PARAMS%% -> str_split( , DTLS_MODE, DTLS_DIGALG, DTLS_DIGSUM)
+fwd: L %%OS_CALLID%% 127.0.0.1 %%OS_PORTO%% from_tag_1 to_tag_1 && M4:1 P %%DTLS_DIGALG%% %%DTLS_DIGSUM%% -> validate_port(OS_PORT2)
+.sleep: 1
+.exec: %%PYINT%% -c "import socket; s=socket.socket(socket.AF_INET,socket.SOCK_DGRAM); [s.sendto(bytes.fromhex('8000%04x%08x00000001' % (q, q * 160))+bytes(n),('127.0.0.1',%%OS_PORT2%%)) for q, n in ((1, 160), (2, 9000), (3, 160))]"
+.eval: npkts_ina=3 nrelayed=2 ndropped=1 -> OS_EXPECTED
+.until: OS_DONE do oversize.check.rptl every 0.1 5
+.eval: 0 -> RES_OK
+fwd: D %%OS_CALLID%% from_tag_1 to_tag_1 -> str_compare(RES_OK)
+geno: D %%OS_CALLID%% from_tag_1 to_tag_1 -> str_compare(RES_OK)