diff --git a/src/buffer/katetextblock.cpp b/src/buffer/katetextblock.cpp
--- a/src/buffer/katetextblock.cpp
+++ b/src/buffer/katetextblock.cpp
@@ -30,6 +30,7 @@
 {
     // reserve the block size
     m_lines.reserve(m_buffer->m_blockSize);
+    m_cachedLineForRanges.reserve(m_buffer->m_blockSize);
 }
 
 TextBlock::~TextBlock()