diff --git a/common/chat-diff-analyzer.cpp b/common/chat-diff-analyzer.cpp
index 2f0bd14afa3..54a998dec05 100644
--- a/common/chat-diff-analyzer.cpp
+++ b/common/chat-diff-analyzer.cpp
@@ -296,7 +296,7 @@ void analyze_reasoning::compare_reasoning_presence() {
             return p.literal(reasoning_content) + p.space() + p.optional(p.tag("post", (p.marker() + p.space())) + p.rest());
         });
         auto parser_wrapped = build_tagged_peg_parser([&](common_peg_parser_builder &p) {
-            return p.tag("pre", p.marker() + p.space()) + p.literal(reasoning_content) + p.space() + p.tag("post", (p.marker() + p.space())) + p.rest();
+            return p.tag("pre", p.marker() + p.space()) + p.literal(reasoning_content) + p.tag("post", (p.space() + p.marker() + p.space())) + p.rest();
         });
         // try the more aggressive parse first, if it fails, fall back to the delimiter one
         auto result = parser_wrapped.parse_anywhere_and_extract(comparison->output_B);
diff --git a/tools/server/server-common.cpp b/tools/server/server-common.cpp
index f66b1f2557c..8539e215bb3 100644
--- a/tools/server/server-common.cpp
+++ b/tools/server/server-common.cpp
@@ -1068,13 +1068,6 @@ json oaicompat_chat_params_parse(
             throw std::invalid_argument("Cannot have 2 or more assistant messages at the end of the list.");
         }
 
-        /* TODO: test this properly */
-        inputs.reasoning_format = COMMON_REASONING_FORMAT_NONE;
-
-        if ( inputs.enable_thinking ) {
-            throw std::invalid_argument("Assistant response prefill is incompatible with enable_thinking.");
-        }
-
         inputs.add_generation_prompt = true;
     }
     inputs.force_pure_content = opt.force_pure_content;
@@ -1084,11 +1077,26 @@ json oaicompat_chat_params_parse(
 
     /* Append assistant prefilled message */
     if (prefill_assistant_message) {
+        auto append_thinking_end = inputs.enable_thinking;
+        if ( append_thinking_end ) {
+            chat_params.prompt += last_message.reasoning_content;
+        }
+        std::string thinking_end = chat_params.thinking_end_tag;
+
         if (!last_message.content_parts.empty()) {
             for (auto & p : last_message.content_parts) {
+                if (p.text.length() > 0 && append_thinking_end) {
+                    chat_params.prompt += thinking_end;
+                    append_thinking_end = false;
+                }
+
                 chat_params.prompt += p.text;
             }
         } else {
+            if (last_message.content.length() > 0 && append_thinking_end) {
+                chat_params.prompt += thinking_end;
+                append_thinking_end = false;
+            }
             chat_params.prompt += last_message.content;
         }
     }