diff --git a/CMakeLists.txt b/CMakeLists.txt
index 50960c01c..8f92690b6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -542,7 +542,6 @@ if(RUN_TESTS)
   include(GoogleTest)
   find_package(GTest REQUIRED)
   target_include_directories(devilutionx-tests PRIVATE ${GTEST_INCLUDE_DIRS})
-  add_definitions(-DRUN_TESTS)
   if(NOT CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
     target_compile_options(devilutionx-tests PRIVATE -fprofile-arcs -ftest-coverage)
   endif()
diff --git a/Source/DiabloUI/dialogs.cpp b/Source/DiabloUI/dialogs.cpp
index c84f0c830..f83774f39 100644
--- a/Source/DiabloUI/dialogs.cpp
+++ b/Source/DiabloUI/dialogs.cpp
@@ -266,15 +266,13 @@ void UiOkDialog(const char *text, const char *caption, bool error, const std::ve
 		if (SDL_ShowCursor(SDL_ENABLE) <= -1) {
 			Log("{}", SDL_GetError());
 		}
-#ifndef RUN_TESTS
-		if (SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, text, caption, nullptr) <= -1) {
-			Log("{}", SDL_GetError());
-#else
-		{
-#endif
-			Log("{}", text);
-			Log("{}", caption);
+		if (!gbQuietMode) {
+			if (SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, text, caption, nullptr) <= -1) {
+				Log("{}", SDL_GetError());
+			}
 		}
+		Log("{}", text);
+		Log("{}", caption);
 		return;
 	}
 
diff --git a/Source/diablo.cpp b/Source/diablo.cpp
index 1c0d886f9..d22ab6fbc 100644
--- a/Source/diablo.cpp
+++ b/Source/diablo.cpp
@@ -109,6 +109,7 @@ bool forceDiablo;
 bool gbNestArt;
 bool gbBard;
 bool gbBarbarian;
+bool gbQuietMode = false;
 int sgnTimeoutCurs;
 clicktype sgbMouseDown;
 int color_cycle_timer;
diff --git a/Source/diablo.h b/Source/diablo.h
index 519c03a3f..854ddf390 100644
--- a/Source/diablo.h
+++ b/Source/diablo.h
@@ -44,6 +44,10 @@ extern int PauseMode;
 extern bool gbNestArt;
 extern bool gbBard;
 extern bool gbBarbarian;
+/**
+ * @brief Don't show Messageboxes or other user-interaction. Needed for UnitTests.
+ */
+extern bool gbQuietMode;
 extern clicktype sgbMouseDown;
 extern uint16_t gnTickDelay;
 extern char gszProductName[64];
diff --git a/test/main.cpp b/test/main.cpp
index b4aa7f06d..e3b60271d 100644
--- a/test/main.cpp
+++ b/test/main.cpp
@@ -1,7 +1,10 @@
 #include <gtest/gtest.h>
 
+#include "diablo.h"
+
 int main(int argc, char **argv)
 {
+	devilution::gbQuietMode = true;
 	testing::InitGoogleTest(&argc, argv);
 	return RUN_ALL_TESTS();
 }