diff --git a/src/providers/deepseek.rs b/src/providers/deepseek.rs
index 207f3f53..7028b6ba 100644
--- a/src/providers/deepseek.rs
+++ b/src/providers/deepseek.rs
@@ -77,10 +77,12 @@ impl super::Provider for DeepSeekProvider {
                     for m in messages {
                         if m["role"] == "assistant" && m.get("tool_calls").is_some() {
                             if m.get("reasoning_content").is_none() || m["reasoning_content"].is_null() {
-                                // DeepSeek R1 requires reasoning_content for tool calls in history.
-                                // If missing (e.g. from client or other model), inject a placeholder.
                                 m["reasoning_content"] = serde_json::json!("Thinking...");
                             }
+                            // DeepSeek R1 often requires content to be a string, not null
+                            if m.get("content").is_none() || m["content"].is_null() {
+                                m["content"] = serde_json::json!("");
+                            }
                         }
                     }
                 }
@@ -100,6 +102,7 @@ impl super::Provider for DeepSeekProvider {
             let status = response.status();
             let error_text = response.text().await.unwrap_or_default();
             tracing::error!("DeepSeek API error ({}): {}", status, error_text);
+            tracing::debug!("DeepSeek Request Body: {}", serde_json::to_string(&body).unwrap_or_default());
             return Err(AppError::ProviderError(format!("DeepSeek API error ({}): {}", status, error_text)));
         }
 
@@ -164,6 +167,10 @@ impl super::Provider for DeepSeekProvider {
                             if m.get("reasoning_content").is_none() || m["reasoning_content"].is_null() {
                                 m["reasoning_content"] = serde_json::json!("Thinking...");
                             }
+                            // DeepSeek R1 often requires content to be a string, not null
+                            if m.get("content").is_none() || m["content"].is_null() {
+                                m["content"] = serde_json::json!("");
+                            }
                         }
                     }
                 }
@@ -218,9 +225,11 @@ impl super::Provider for DeepSeekProvider {
                         match probe_resp {
                             Ok(r) if !r.status().is_success() => {
                                 let status = r.status();
-                                let body = r.text().await.unwrap_or_default();
-                                tracing::error!("DeepSeek Stream Error Probe ({}): {}", status, body);
-                                Err(AppError::ProviderError(format!("DeepSeek API error ({}): {}", status, body)))?;
+                                let error_body = r.text().await.unwrap_or_default();
+                                tracing::error!("DeepSeek Stream Error Probe ({}): {}", status, error_body);
+                                // Log the offending request body at debug level (it's large)
+                                tracing::debug!("Offending DeepSeek Request Body: {}", serde_json::to_string(&probe_body).unwrap_or_default());
+                                Err(AppError::ProviderError(format!("DeepSeek API error ({}): {}", status, error_body)))?;
                             }
                             _ => {
                                 Err(AppError::ProviderError(format!("Stream error: {}", e)))?;
diff --git a/src/providers/helpers.rs b/src/providers/helpers.rs
index 8e68b34e..86759389 100644
--- a/src/providers/helpers.rs
+++ b/src/providers/helpers.rs
@@ -65,10 +65,10 @@ pub async fn messages_to_openai_json(messages: &[UnifiedMessage]) -> Result<Vec<
             msg["reasoning_content"] = serde_json::json!(reasoning);
         }
 
-        // For assistant messages with tool_calls, content can be null
+        // For assistant messages with tool_calls, content can be empty string
         if let Some(tool_calls) = &m.tool_calls {
             if parts.is_empty() {
-                msg["content"] = serde_json::Value::Null;
+                msg["content"] = serde_json::json!("");
             } else {
                 msg["content"] = serde_json::json!(parts);
             }
@@ -143,10 +143,10 @@ pub async fn messages_to_openai_json_text_only(
             msg["reasoning_content"] = serde_json::json!(reasoning);
         }
 
-        // For assistant messages with tool_calls, content can be null
+        // For assistant messages with tool_calls, content can be empty string
         if let Some(tool_calls) = &m.tool_calls {
             if parts.is_empty() {
-                msg["content"] = serde_json::Value::Null;
+                msg["content"] = serde_json::json!("");
             } else {
                 msg["content"] = serde_json::json!(parts);
             }