diff --git a/navi/llm/ollama.py b/navi/llm/ollama.py
index 5f805df..d164fe1 100644
--- a/navi/llm/ollama.py
+++ b/navi/llm/ollama.py
@@ -11,12 +11,28 @@
 from .base import LLMBackend, LLMChunk, LLMResponse, Message, ToolCallRequest, ToolSchema
 
 
+def _clean_base64_image(img: str) -> str | None:
+    """Strip data URI prefix and validate that result is non-empty base64."""
+    if not img:
+        return None
+    s = img.strip()
+    if s.startswith("data:"):
+        if "," in s:
+            s = s.split(",", 1)[1]
+        else:
+            return None
+    return s if s else None
+
+
 def _to_ollama_messages(messages: list[Message]) -> list[dict]:
     result = []
     for m in messages:
         msg: dict = {"role": m.role, "content": m.content or ""}
         if m.images:
-            msg["images"] = m.images  # list of base64 strings, Ollama format
+            cleaned = [_clean_base64_image(img) for img in m.images]
+            cleaned = [img for img in cleaned if img is not None]
+            if cleaned:
+                msg["images"] = cleaned
         if m.tool_calls:
             msg["tool_calls"] = [
                 {"function": {"name": tc.name, "arguments": tc.arguments}}