diff --git a/ovn/lib/actions.c b/ovn/lib/actions.c
index 2bc495c..0874174 100644
--- a/ovn/lib/actions.c
+++ b/ovn/lib/actions.c
@@ -205,6 +205,15 @@ parse_actions(struct action_context *ctx)
             parse_next_action(ctx);
         } else if (lexer_match_id(ctx->lexer, "output")) {
             emit_resubmit(ctx, ctx->output_table);
+        } else if (lexer_match_id(ctx->lexer, "ip4.ttl")) {
+            if (lexer_match(ctx->lexer, LEX_T_DECREMENT)) {
+                struct expr *e = expr_parse_string("ip4", ctx->symtab,
+                                                   &ctx->error);
+                ctx->prereqs = expr_combine(EXPR_T_AND, ctx->prereqs, e);
+                ofpact_put_DEC_TTL(ctx->ofpacts);
+            } else {
+                action_syntax_error(ctx, "expecting `--'");
+            }
         } else {
             action_syntax_error(ctx, "expecting action");
         }
diff --git a/ovn/lib/lex.c b/ovn/lib/lex.c
index 308d216..cc8eb28 100644
--- a/ovn/lib/lex.c
+++ b/ovn/lib/lex.c
@@ -241,6 +241,9 @@ lex_token_format(const struct lex_token *token, struct ds *s)
     case LEX_T_EXCHANGE:
         ds_put_cstr(s, "<->");
         break;
+    case LEX_T_DECREMENT:
+        ds_put_cstr(s, "--");
+        break;
     default:
         OVS_NOT_REACHED();
     }
@@ -640,6 +643,16 @@ next:
         token->type = LEX_T_SEMICOLON;
         break;
 
+    case '-':
+        p++;
+        if (*p == '-') {
+            token->type = LEX_T_DECREMENT;
+            p++;
+        } else {
+            lex_error(token, "`-' is only valid as part of `--'.");
+        }
+        break;
+
     case '0': case '1': case '2': case '3': case '4':
     case '5': case '6': case '7': case '8': case '9':
     case ':':
diff --git a/ovn/lib/lex.h b/ovn/lib/lex.h
index 7ad6f55..3c2bb6a 100644
--- a/ovn/lib/lex.h
+++ b/ovn/lib/lex.h
@@ -59,6 +59,7 @@ enum lex_type {
     LEX_T_SEMICOLON,            /* ; */
     LEX_T_EQUALS,               /* = */
     LEX_T_EXCHANGE,             /* <-> */
+    LEX_T_DECREMENT,            /* -- */
 };
 
 /* Subtype for LEX_T_INTEGER and LEX_T_MASKED_INTEGER tokens.
diff --git a/tests/ovn.at b/tests/ovn.at
index 330f723..095b0d9 100644
--- a/tests/ovn.at
+++ b/tests/ovn.at
@@ -82,9 +82,10 @@ fe:x => error("Invalid numeric constant.")
 00:01:02:03:04:x => error("Invalid numeric constant.")
 
 # Test that operators are tokenized as expected, even without white space.
-(){}[[]]==!=<<=>>=!&&||..,;=<-> => ( ) { } [[ ]] == != < <= > >= ! && || .. , ; = <->
+(){}[[]]==!=<<=>>=!&&||..,;=<->-- => ( ) { } [[ ]] == != < <= > >= ! && || .. , ; = <-> --
 & => error("`&' is only valid as part of `&&'.")
 | => error("`|' is only valid as part of `||'.")
+- => error("`-' is only valid as part of `--'.")
 
 ^ => error("Invalid character `^' in input.")
 ])
@@ -455,6 +456,8 @@ reg0 <-> reg1; => actions=push:OXM_OF_PKT_REG0[0..31],push:OXM_OF_PKT_REG0[32..6
 vlan.pcp <-> reg0[0..2]; => actions=push:OXM_OF_PKT_REG0[32..34],push:NXM_OF_VLAN_TCI[13..15],pop:OXM_OF_PKT_REG0[32..34],pop:NXM_OF_VLAN_TCI[13..15], prereqs=vlan.tci[12]
 reg0[10] <-> vlan.pcp[1]; => actions=push:NXM_OF_VLAN_TCI[14],push:OXM_OF_PKT_REG0[42],pop:NXM_OF_VLAN_TCI[14],pop:OXM_OF_PKT_REG0[42], prereqs=vlan.tci[12]
 outport <-> inport; => actions=push:NXM_NX_REG6[],push:NXM_NX_REG7[],pop:NXM_NX_REG6[],pop:NXM_NX_REG7[], prereqs=1
+ip4.ttl--; => actions=dec_ttl, prereqs=ip4
+
 # Contradictionary prerequisites (allowed but not useful):
 ip4.src = ip6.src[0..31]; => actions=move:NXM_NX_IPV6_SRC[0..31]->NXM_OF_IP_SRC[], prereqs=eth.type == 0x800 && eth.type == 0x86dd
 ip4.src <-> ip6.src[0..31]; => actions=push:NXM_NX_IPV6_SRC[0..31],push:NXM_OF_IP_SRC[],pop:NXM_NX_IPV6_SRC[0..31],pop:NXM_OF_IP_SRC[], prereqs=eth.type == 0x800 && eth.type == 0x86dd
@@ -498,6 +501,7 @@ inport <-> reg0; => Can't exchange string field (inport) with integer field (reg
 inport <-> big_string; => String fields inport and big_string are incompatible for exchange.
 ip.proto <-> reg0[0..7]; => Field ip.proto is not modifiable.
 reg0[0..7] <-> ip.proto; => Field ip.proto is not modifiable.
+ip4.ttl => Syntax error at end of input expecting `--'.
 ]])
 sed 's/ =>.*//' test-cases.txt > input.txt
 sed 's/.* => //' test-cases.txt > expout
