diff --git a/frontend/pbc_dump/main.c b/frontend/pbc_dump/main.c
index a369421..878adef 100644
--- a/frontend/pbc_dump/main.c
+++ b/frontend/pbc_dump/main.c
@@ -308,11 +308,12 @@ static struct longopt_opt_decl opt_options[] = {
     { 't', 't', OPTION_optional_FLAG, { "--terse"       } },
     { 'n', 'n', OPTION_optional_FLAG, { "--line-nums"   } },
     { 'd', 'd', OPTION_optional_FLAG, { "--disassemble" } },
-    { 'o', 'o', OPTION_required_FLAG, { "--output"      } }
+    { 'o', 'o', OPTION_required_FLAG, { "--output"      } },
 
 #if TRACE_PACKFILE
     { 'D', 'D', OPTION_required_FLAG, { "--debug"       } },
 #endif
+    { 0,    0,  OPTION_optional_FLAG, { NULL            } }
 };
 
 
diff --git a/frontend/pbc_merge/main.c b/frontend/pbc_merge/main.c
index 2c63b79..49d5206 100644
--- a/frontend/pbc_merge/main.c
+++ b/frontend/pbc_merge/main.c
@@ -893,7 +893,8 @@ merge process and finally writes out the produced packfile.
 */
 
 static struct longopt_opt_decl options[] = {
-    { 'o', 'o', OPTION_required_FLAG, { "--output" } }
+    { 'o', 'o', OPTION_required_FLAG, { "--output" } },
+    {  0 ,  0 , OPTION_optional_FLAG, { NULL       } }
 };
 
 int