diff --git a/src/mitm/modify.rs b/src/mitm/modify.rs
index a056150..c73c301 100644
--- a/src/mitm/modify.rs
+++ b/src/mitm/modify.rs
@@ -156,6 +156,7 @@ pub fn modify_request(body: &[u8], tool_ctx: Option<&ToolContext>) -> Option<Vec
     }
 
     // ── 3. Strip LS tools, inject client tools ─────────────────────────────
+    let mut has_custom_tools = false;
     if STRIP_ALL_TOOLS {
         if let Some(tools) = json
             .pointer_mut("/request/tools")
@@ -173,12 +174,45 @@ pub fn modify_request(body: &[u8], tool_ctx: Option<&ToolContext>) -> Option<Vec
                     for tool in custom_tools {
                         tools.push(tool.clone());
                     }
+                    has_custom_tools = true;
                     changes.push(format!("inject {} custom tool group(s)", custom_tools.len()));
                 }
             }
         }
     }
 
+    // ── 3a. Strip functionCall/functionResponse from history when no tools ──
+    // When LS tools are stripped and no custom tools are injected, the model
+    // may try to reference LS tools from conversation history, causing Google
+    // to return MALFORMED_FUNCTION_CALL in an infinite retry loop.
+    if STRIP_ALL_TOOLS && !has_custom_tools {
+        if let Some(contents) = json
+            .pointer_mut("/request/contents")
+            .and_then(|v| v.as_array_mut())
+        {
+            let mut stripped_fc = 0usize;
+            for msg in contents.iter_mut() {
+                if let Some(parts) = msg.get_mut("parts").and_then(|v| v.as_array_mut()) {
+                    let before = parts.len();
+                    parts.retain(|part| {
+                        !part.get("functionCall").is_some()
+                            && !part.get("functionResponse").is_some()
+                    });
+                    stripped_fc += before - parts.len();
+                }
+            }
+            // Remove messages that became empty after stripping function parts
+            contents.retain(|msg| {
+                msg.get("parts")
+                    .and_then(|v| v.as_array())
+                    .map_or(true, |parts| !parts.is_empty())
+            });
+            if stripped_fc > 0 {
+                changes.push(format!("strip {stripped_fc} functionCall/Response parts from history"));
+            }
+        }
+    }
+
     // Inject toolConfig if provided
     if let Some(ref ctx) = tool_ctx {
         if let Some(ref config) = ctx.tool_config {