diff --git a/rcl/include/rcl/lexer.h b/rcl/include/rcl/lexer.h
index ae61b839e..a818fea0b 100644
--- a/rcl/include/rcl/lexer.h
+++ b/rcl/include/rcl/lexer.h
@@ -30,7 +30,7 @@ extern "C"
 /// Type of lexeme found by lexical analysis.
 typedef enum rcl_lexeme_t
 {
-  /// Indicates no valid lexeme was found
+  /// Indicates no valid lexeme was found (end of input not reached)
   RCL_LEXEME_NONE = 0,
   /// Indicates end of input has been reached
   RCL_LEXEME_EOF = 1,
diff --git a/rcl/src/rcl/arguments.c b/rcl/src/rcl/arguments.c
index 7a60c9012..58224a545 100644
--- a/rcl/src/rcl/arguments.c
+++ b/rcl/src/rcl/arguments.c
@@ -110,7 +110,8 @@ rcl_parse_arguments(
     if (RCL_RET_OK == _rcl_parse_remap_rule(argv[i], allocator, rule)) {
       ++(args_impl->num_remap_rules);
     } else {
-      RCUTILS_LOG_DEBUG_NAMED(ROS_PACKAGE_NAME, "arg %d error '%s'", i, rcl_get_error_string());
+      RCUTILS_LOG_DEBUG_NAMED(ROS_PACKAGE_NAME, "arg %d (%s) error '%s'", i, argv[i],
+        rcl_get_error_string());
       rcl_reset_error();
       args_impl->unparsed_args[args_impl->num_unparsed_args] = i;
       ++(args_impl->num_unparsed_args);
@@ -656,6 +657,19 @@ _rcl_parse_remap_namespace_replacement(
   }
   ret = _rcl_parse_remap_fully_qualified_namespace(lex_lookahead);
   if (RCL_RET_OK != ret) {
+    if (RCL_RET_INVALID_REMAP_RULE == ret) {
+      // The name didn't start with a leading forward slash
+      RCUTILS_LOG_WARN_NAMED(
+        ROS_PACKAGE_NAME, "Namespace not remapped to a fully qualified name (found: %s)", ns_start);
+    }
+    return ret;
+  }
+  // There should be nothing left
+  ret = rcl_lexer_lookahead2_expect(lex_lookahead, RCL_LEXEME_EOF, NULL, NULL);
+  if (RCL_RET_OK != ret) {
+    // The name must have started with a leading forward slash but had an otherwise invalid format
+    RCUTILS_LOG_WARN_NAMED(
+      ROS_PACKAGE_NAME, "Namespace not remapped to a fully qualified name (found: %s)", ns_start);
     return ret;
   }
 
diff --git a/rcl/src/rcl/lexer_lookahead.c b/rcl/src/rcl/lexer_lookahead.c
index f2c882152..cfc2fe4f3 100644
--- a/rcl/src/rcl/lexer_lookahead.c
+++ b/rcl/src/rcl/lexer_lookahead.c
@@ -222,8 +222,15 @@ rcl_lexer_lookahead2_expect(
     return ret;
   }
   if (type != lexeme) {
+    if (RCL_LEXEME_NONE == lexeme || RCL_LEXEME_EOF == lexeme) {
+      RCL_SET_ERROR_MSG_WITH_FORMAT_STRING(
+        buffer->impl->allocator, "Expected lexeme type (%d) not found, search ended at index %lu",
+        type, buffer->impl->text_idx);
+      return RCL_RET_WRONG_LEXEME;
+    }
     RCL_SET_ERROR_MSG_WITH_FORMAT_STRING(
-      buffer->impl->allocator, "Expected %d got %d at %lu", type, lexeme, buffer->impl->text_idx);
+      buffer->impl->allocator, "Expected lexeme type %d, got %d at index %lu", type, lexeme,
+      buffer->impl->text_idx);
     return RCL_RET_WRONG_LEXEME;
   }
   return rcl_lexer_lookahead2_accept(buffer, lexeme_text, lexeme_text_length);