diff --git a/src/working_files.cc b/src/working_files.cc
index 93354640..5c01b4b3 100644
--- a/src/working_files.cc
+++ b/src/working_files.cc
@@ -74,9 +74,11 @@ optional<int> WorkingFile::GetBufferLineFromIndexLine(int index_line) const {
   // Note: |index_line| and |buffer_line| are 1-based.
 
   // TODO: reenable this assert once we are using the real indexed file.
-  assert(index_line >= 1 && index_line <= index_lines.size());
-  //if (index_line < 1 || index_line > index_lines.size())
-  //  return nullopt;
+  //assert(index_line >= 1 && index_line <= index_lines.size());
+  if (index_line < 1 || index_line > index_lines.size()) {
+    std::cerr << "!! Bad index_line (got " << index_line << ", expected [1, " << index_lines.size() << "])" << std::endl;
+    return nullopt;
+  }
 
   // Find the line in the cached index file. We'll try to find the most similar line
   // in the buffer and return the index for that.
@@ -108,9 +110,11 @@ optional<int> WorkingFile::GetIndexLineFromBufferLine(int buffer_line) const {
   // See GetBufferLineFromIndexLine for additional comments.
 
   // Note: |index_line| and |buffer_line| are 1-based.
-  assert(buffer_line >= 1 && buffer_line < all_buffer_lines.size());
-  //if (buffer_line < 1 || buffer_line > all_buffer_lines.size())
-  //  return nullopt;
+  //assert(buffer_line >= 1 && buffer_line < all_buffer_lines.size());
+  if (buffer_line < 1 || buffer_line > all_buffer_lines.size()) {
+    std::cerr << "!! Bad buffer_line (got " << buffer_line << ", expected [1, " << all_buffer_lines.size() << "])" << std::endl;
+    return nullopt;
+  }
 
   // Find the line in the index file. We'll try to find the most similar line
   // in the index file and return the index for that.