diff --git a/lua/gemini/completion.lua b/lua/gemini/completion.lua
index fce4b5c..fbc234a 100644
--- a/lua/gemini/completion.lua
+++ b/lua/gemini/completion.lua
@@ -63,19 +63,32 @@ local function show_suggestion(suggestion, start_col)
     
     -- Process first line of suggestion
     local first_line = suggestion_lines[1]
-    if not first_line:find("^" .. vim.pesc(prefix), 1, true) then
-        first_line = prefix .. first_line
+    
+    -- Find the longest common prefix between the input and suggestion
+    local common_length = 0
+    local input_after_cursor = string.sub(line_text, start_col + 1)
+    local suggestion_text = first_line
+    
+    while common_length < #input_after_cursor and common_length < #suggestion_text do
+        if string.sub(input_after_cursor, common_length + 1, common_length + 1) ==
+           string.sub(suggestion_text, common_length + 1, common_length + 1) then
+            common_length = common_length + 1
+        else
+            break
+        end
     end
-    first_line = first_line:sub(#prefix + 1)
+    
+    -- Only show the part of suggestion that doesn't overlap with existing text
+    first_line = string.sub(suggestion_text, common_length + 1)
     
     if first_line == "" and #suggestion_lines == 1 then return end
     
     current_suggestion.text = suggestion
     current_suggestion.start_col = start_col
     
-    -- Show first line as virtual text
+    -- Show first line as virtual text only if there's non-overlapping content
     if first_line ~= "" then
-        vim.api.nvim_buf_set_extmark(0, current_suggestion.namespace_id, line, start_col, {
+        vim.api.nvim_buf_set_extmark(0, current_suggestion.namespace_id, line, start_col + common_length, {
             virt_text = {{first_line, 'GeminiSuggestion'}},
             virt_text_pos = 'inline',
             virt_text_hide = true,
@@ -89,13 +102,13 @@ local function show_suggestion(suggestion, start_col)
             table.insert(virt_lines, {{suggestion_lines[i], 'GeminiSuggestion'}})
         end
         
-        vim.api.nvim_buf_set_extmark(0, current_suggestion.namespace_id, line, start_col, {
+        vim.api.nvim_buf_set_extmark(0, current_suggestion.namespace_id, line, start_col + common_length, {
             virt_lines = virt_lines,
             virt_lines_above = false,
         })
     end
     
-    debug_print("Showing suggestion (%d lines)", #suggestion_lines)
+    debug_print("Showing suggestion (%d lines, common prefix length: %d)", #suggestion_lines, common_length)
 end
 
 function M.accept_suggestion()
@@ -111,19 +124,38 @@ function M.accept_suggestion()
         return false
     end
     
+    -- Get current line text
+    local line_text = vim.api.nvim_buf_get_lines(0, line, line + 1, true)[1]
+    local text_after_cursor = string.sub(line_text, col + 1)
+    
     -- Split suggestion into lines
     local suggestion_lines = vim.split(current_suggestion.text, "\n")
     if #suggestion_lines == 0 then return false end
     
-    -- Insert first line at cursor position
-    vim.api.nvim_buf_set_text(
-        0,
-        line,
-        col,
-        line,
-        col,
-        {suggestion_lines[1]}
-    )
+    -- For the first line, only insert the part that doesn't overlap with existing text
+    local first_line = suggestion_lines[1]
+    local common_length = 0
+    while common_length < #text_after_cursor and common_length < #first_line do
+        if string.sub(text_after_cursor, common_length + 1, common_length + 1) ==
+           string.sub(first_line, common_length + 1, common_length + 1) then
+            common_length = common_length + 1
+        else
+            break
+        end
+    end
+    
+    -- Only insert the non-overlapping part
+    local to_insert = string.sub(first_line, common_length + 1)
+    if to_insert ~= "" then
+        vim.api.nvim_buf_set_text(
+            0,
+            line,
+            col,
+            line,
+            col,
+            {to_insert}
+        )
+    end
     
     -- Insert remaining lines below
     if #suggestion_lines > 1 then
@@ -138,7 +170,12 @@ function M.accept_suggestion()
     
     -- Move cursor to end of inserted text
     local final_line = line + #suggestion_lines - 1
-    local final_col = #suggestion_lines[#suggestion_lines]
+    local final_col
+    if final_line == line then
+        final_col = col + #to_insert
+    else
+        final_col = #suggestion_lines[#suggestion_lines]
+    end
     vim.api.nvim_win_set_cursor(0, {final_line + 1, final_col})
     
     clear_suggestion()