diff --git a/common/chat.cpp b/common/chat.cpp
index ef151691c..4401225c5 100644
--- a/common/chat.cpp
+++ b/common/chat.cpp
@@ -1116,15 +1116,21 @@ static common_chat_params common_chat_params_init_gpt_oss(const common_chat_temp
     auto extract_reasoning   = inputs.reasoning_format != COMMON_REASONING_FORMAT_NONE;
 
     auto parser = build_chat_peg_parser([&](common_chat_peg_builder & p) {
-        auto start           = p.rule("start", p.literal("<|start|>assistant"));
+        // llm-jp-4 thinking models emit a stray leading space after
+        // <|start|>/<|channel|> (add_space_prefix detokenization), e.g.
+        // "<|channel|> analysis<|message|>" instead of the canonical
+        // "<|channel|>analysis<|message|>". Tolerate an optional space
+        // right after those special tokens so the peg-native rules match.
+        auto opt_space       = p.optional(p.space());
+        auto start           = p.rule("start", p.literal("<|start|>") + opt_space + p.literal("assistant"));
         auto end             = p.rule("end", p.literal("<|end|>"));
         auto content         = p.rule("message-content", p.until("<|end|>"));
-        auto channel         = p.literal("<|channel|>") + (p.literal("commentary") | p.literal("analysis"));
+        auto channel         = p.literal("<|channel|>") + opt_space + (p.literal("commentary") | p.literal("analysis"));
         auto constrain_type  = p.chars("[A-Za-z0-9_-]", 1, -1);
 
         // Occasionally, gpt-oss-20b will prefix channels with this commentary
-        auto stray_commentary = p.optional(p.literal("<|channel|>commentary") + p.optional(p.literal(" to=assistant")));
-        auto start_analysis = stray_commentary + p.literal("<|channel|>analysis<|message|>");
+        auto stray_commentary = p.optional(p.literal("<|channel|>") + opt_space + p.literal("commentary") + p.optional(p.literal(" to=assistant")));
+        auto start_analysis = stray_commentary + p.literal("<|channel|>") + opt_space + p.literal("analysis<|message|>");
 
         if (extract_reasoning) {
             p.rule("analysis", start_analysis + p.reasoning(content) + end);
@@ -1133,8 +1139,8 @@ static common_chat_params common_chat_params_init_gpt_oss(const common_chat_temp
         }
 
         auto analysis = p.ref("analysis");
-        auto preamble = p.rule("preamble", p.literal("<|channel|>commentary<|message|>") + p.content(content) + end);
-        auto final_msg = p.rule("final", stray_commentary + p.literal("<|channel|>final<|message|>") + p.content(content));
+        auto preamble = p.rule("preamble", p.literal("<|channel|>") + opt_space + p.literal("commentary<|message|>") + p.content(content) + end);
+        auto final_msg = p.rule("final", stray_commentary + p.literal("<|channel|>") + opt_space + p.literal("final<|message|>") + p.content(content));
 
         // Consume any unsolicited tool calls, e.g. builtin functions
         auto unsolicited = p.rule("unsolicited", p.atomic(p.optional(channel) + p.literal(" to=") + content + end));
@@ -1144,7 +1150,7 @@ static common_chat_params common_chat_params_init_gpt_oss(const common_chat_temp
         if (has_response_format) {
             auto constraint = p.optional(p.space() + p.optional(p.literal("<|constrain|>")) + constrain_type);
             auto response_format = p.rule("response-format",
-                p.literal("<|channel|>final") + constraint + p.literal("<|message|>") +
+                p.literal("<|channel|>") + opt_space + p.literal("final") + constraint + p.literal("<|message|>") +
                 p.content(p.schema(p.json(), "response-format-schema", inputs.json_schema)));
 
             return p.zero_or_more(start + analysis) + start + response_format;
@@ -1164,11 +1170,11 @@ static common_chat_params common_chat_params_init_gpt_oss(const common_chat_temp
 
                 // recipient in role header
                 //   <|start|>assistant to=functions.NAME<|channel|>(commentary|analysis)[constraint]<|message|>ARGS
-                auto tool_in_role = p.tool(p.tool_open(func_name + channel + constraint + p.literal("<|message|>")) + args);
+                auto tool_in_role = p.tool(p.tool_open(func_name + channel + constraint + opt_space + p.literal("<|message|>")) + args);
 
                 // recipient in channel header
                 //   <|channel|>(commentary|analysis) to=functions.NAME[constraint]<|message|>ARGS
-                auto tool_in_channel = p.tool(p.tool_open(channel + func_name + constraint + p.literal("<|message|>")) + args);
+                auto tool_in_channel = p.tool(p.tool_open(channel + func_name + constraint + opt_space + p.literal("<|message|>")) + args);
 
                 tool_choice |= p.rule("tool-" + name, tool_in_role | tool_in_channel);
             });