diff --git a/Source/CMakeLists.txt b/Source/CMakeLists.txt
index 112b4569227..3a2a415ed51 100644
--- a/Source/CMakeLists.txt
+++ b/Source/CMakeLists.txt
@@ -169,6 +169,21 @@ set(libdevilutionx_SRCS
   utils/timer.cpp
   utils/utf8.cpp)
 
+# These files are responsible for most of the runtime in Debug mode.
+# Apply some optimizations to them even in Debug mode to get reasonable performance.
+set(_optimize_in_debug_srcs
+  engine/render/clx_render.cpp
+  engine/render/dun_render.cpp
+  engine/render/text_render.cpp
+  utils/cel_to_clx.cpp
+  utils/cl2_to_clx.cpp
+  utils/pcx_to_clx.cpp)
+if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang" AND CMAKE_BUILD_TYPE STREQUAL "Debug")
+  set_source_files_properties(${_optimize_in_debug_srcs} PROPERTIES COMPILE_OPTIONS "-O2")
+elseif(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+  set_source_files_properties(${_optimize_in_debug_srcs} PROPERTIES COMPILE_OPTIONS "$<$<CONFIG:Debug>:/O2>")
+endif()
+
 if(SUPPORTS_MPQ)
   list(APPEND libdevilutionx_DEPS libmpq)
   list(APPEND libdevilutionx_SRCS