diff --git a/apps/apps.h b/apps/apps.h
index 319b02ef1948e3e9dd6a85109b7e85e4e141d0ff..5faf440200bd9bd31a8916104311dcb6a59f663b 100644
--- a/apps/apps.h
+++ b/apps/apps.h
@@ -274,6 +274,10 @@ int has_stdin_waiting(void);
         case OPT_S_DHPARAM: \
         case OPT_S_DEBUGBROKE
 
+#define IS_NO_PROT_FLAG(o) \
+ (o == OPT_S_NOSSL3 || o == OPT_S_NOTLS1 || o == OPT_S_NOTLS1_1 \
+  || o == OPT_S_NOTLS1_2)
+
 /*
  * Option parsing.
  */
diff --git a/apps/s_client.c b/apps/s_client.c
index e79cf7e496e3161124f441699c6bf24091780a0c..69e225cef63d3c3f369a9b6e66ab40ab921e2e2c 100644
--- a/apps/s_client.c
+++ b/apps/s_client.c
@@ -768,6 +768,10 @@ static const OPT_PAIR services[] = {
  (o == OPT_4 || o == OPT_6 || o == OPT_HOST || o == OPT_PORT || o == OPT_CONNECT)
 #define IS_UNIX_FLAG(o) (o == OPT_UNIX)
 
+#define IS_PROT_FLAG(o) \
+ (o == OPT_SSL3 || o == OPT_TLS1 || o == OPT_TLS1_1 || o == OPT_TLS1_2 \
+  || o == OPT_DTLS || o == OPT_DTLS1 || o == OPT_DTLS1_2)
+
 /* Free |*dest| and optionally set it to a copy of |source|. */
 static void freeandcopy(char **dest, const char *source)
 {
@@ -851,7 +855,7 @@ int s_client_main(int argc, char **argv)
     char *ctlog_file = NULL;
     int ct_validation = 0;
 #endif
-    int min_version = 0, max_version = 0;
+    int min_version = 0, max_version = 0, prot_opt = 0, no_prot_opt = 0;
     int async = 0;
     unsigned int split_send_fragment = 0;
     unsigned int max_pipelines = 0;
@@ -905,6 +909,19 @@ int s_client_main(int argc, char **argv)
                 prog);
             goto end;
         }
+
+        if (IS_PROT_FLAG(o) && ++prot_opt > 1) {
+            BIO_printf(bio_err, "Cannot supply multiple protocol flags\n");
+            goto end;
+        }
+        if (IS_NO_PROT_FLAG(o))
+            no_prot_opt++;
+        if (prot_opt == 1 && no_prot_opt) {
+            BIO_printf(bio_err, "Cannot supply both a protocol flag and "
+                                "\"-no_<prot>\"\n");
+            goto end;
+        }
+
         switch (o) {
         case OPT_EOF:
         case OPT_ERR:
diff --git a/apps/s_server.c b/apps/s_server.c
index 45c128d70129878f27c3f00a024ccba3ebe296f2..d545546f29d0d3bf01a75850f6278ff4f7fad014 100644
--- a/apps/s_server.c
+++ b/apps/s_server.c
@@ -910,6 +910,10 @@ OPTIONS s_server_options[] = {
     {NULL, OPT_EOF, 0, NULL}
 };
 
+#define IS_PROT_FLAG(o) \
+ (o == OPT_SSL3 || o == OPT_TLS1 || o == OPT_TLS1_1 || o == OPT_TLS1_2 \
+  || o == OPT_DTLS || o == OPT_DTLS1 || o == OPT_DTLS1_2)
+
 int s_server_main(int argc, char *argv[])
 {
     ENGINE *engine = NULL;
@@ -970,7 +974,7 @@ int s_server_main(int argc, char *argv[])
     char *srpuserseed = NULL;
     char *srp_verifier_file = NULL;
 #endif
-    int min_version = 0, max_version = 0;
+    int min_version = 0, max_version = 0, prot_opt = 0, no_prot_opt = 0;
 
     local_argc = argc;
     local_argv = argv;
@@ -984,6 +988,17 @@ int s_server_main(int argc, char *argv[])
 
     prog = opt_init(argc, argv, s_server_options);
     while ((o = opt_next()) != OPT_EOF) {
+        if (IS_PROT_FLAG(o) && ++prot_opt > 1) {
+            BIO_printf(bio_err, "Cannot supply multiple protocol flags\n");
+            goto end;
+        }
+        if (IS_NO_PROT_FLAG(o))
+            no_prot_opt++;
+        if (prot_opt == 1 && no_prot_opt) {
+            BIO_printf(bio_err, "Cannot supply both a protocol flag and "
+                                "\"-no_<prot>\"\n");
+            goto end;
+        }
         switch (o) {
         case OPT_EOF:
         case OPT_ERR: