diff --git a/lib-api.cpp b/lib-api.cpp
index 2a0a92e..4385088 100644
--- a/lib-api.cpp
+++ b/lib-api.cpp
@@ -235,6 +235,7 @@ void locoAcquiredGotFunc(LocoInfo locoInfo, TrkAcquiredCallback acquired, void *
 
 	if (acquired != nullptr)
 		acquired(&lib.xn, locoInfo);
+	// When >O0, segfault happens in the return below (don't know why).
 }
 
 void locoAcquired(LocoAddr addr, TrkAcquiredCallback acquired, LibStdCallback err,
diff --git a/xn.pro b/xn.pro
index 485f073..2d0aebb 100644
--- a/xn.pro
+++ b/xn.pro
@@ -55,3 +55,8 @@ DEFINES += "VERSION_MAJOR=$$VERSION_MAJOR" \
 #Target version
 VERSION = $${VERSION_MAJOR}.$${VERSION_MINOR}
 DEFINES += "VERSION=\\\"$${VERSION}\\\""
+
+
+#When >=O1, segfault happens in lib-api.cpp
+QMAKE_CXXFLAGS_RELEASE -= -O2
+QMAKE_CXXFLAGS_RELEASE += -O0