diff --git a/src/gui/CMakeLists.txt b/src/gui/CMakeLists.txt
index 63aa790..0b01d34 100644
--- a/src/gui/CMakeLists.txt
+++ b/src/gui/CMakeLists.txt
@@ -68,4 +68,5 @@ endif()
 
 
 add_subdirectory(ui)
+add_subdirectory(tests)
 
diff --git a/src/gui/tests/CMakeLists.txt b/src/gui/tests/CMakeLists.txt
new file mode 100644
index 0000000..3aefcff
--- /dev/null
+++ b/src/gui/tests/CMakeLists.txt
@@ -0,0 +1,21 @@
+###############################################################################
+# License: BSD Zero Clause License file
+# Copyright:
+#   (C) 2026 Alexander Shaduri <ashaduri@gmail.com>
+###############################################################################
+
+if (NOT APP_BUILD_TESTS)
+    set_directory_properties(PROPERTIES EXCLUDE_FROM_ALL true)
+else()
+    set_directory_properties(PROPERTIES EXCLUDE_FROM_ALL false)
+endif()
+
+
+# Use Object libraries to allow runtime test discovery
+add_library(gui_tests OBJECT)
+target_sources(gui_tests PRIVATE
+	test_fractional_scaling.cpp
+)
+target_link_libraries(gui_tests PRIVATE
+	Catch2
+)
diff --git a/src/gui/tests/test_fractional_scaling.cpp b/src/gui/tests/test_fractional_scaling.cpp
new file mode 100644
index 0000000..dfe8bee
--- /dev/null
+++ b/src/gui/tests/test_fractional_scaling.cpp
@@ -0,0 +1,216 @@
+/******************************************************************************
+License: BSD Zero Clause License
+Copyright:
+	(C) 2008 - 2026 Alexander Shaduri <ashaduri@gmail.com>
+******************************************************************************/
+/// \file
+/// \author Alexander Shaduri
+/// \ingroup gui_tests
+/// \weakgroup gui_tests
+/// @{
+
+#include "catch2/catch.hpp"
+
+#include <cmath>
+
+
+/// Test the fractional scaling calculation logic
+/// This tests the mathematical correctness of the scaling correction ratio
+TEST_CASE("FractionalScalingCalculation", "[gui][scaling]")
+{
+	// Test the calculation logic that's used in app_apply_fractional_scaling_to_default_size()
+	// correction = system_scale / integer_ui_scale
+
+	SECTION("125% scaling (fractional)")
+	{
+		const int full_percent = 125;
+		const double system_scale = static_cast<double>(full_percent) / 100.0;  // 1.25
+		const int integer_ui_scale = full_percent / 100;  // 1
+		const double correction = system_scale / static_cast<double>(integer_ui_scale);
+
+		REQUIRE(system_scale == 1.25);
+		REQUIRE(integer_ui_scale == 1);
+		REQUIRE(correction == 1.25);
+
+		// Test window scaling: 800x600 base should become 1000x750
+		const int base_w = 800;
+		const int base_h = 600;
+		const int scaled_w = static_cast<int>(std::lround(base_w * correction));
+		const int scaled_h = static_cast<int>(std::lround(base_h * correction));
+
+		REQUIRE(scaled_w == 1000);
+		REQUIRE(scaled_h == 750);
+	}
+
+	SECTION("150% scaling (fractional)")
+	{
+		const int full_percent = 150;
+		const double system_scale = static_cast<double>(full_percent) / 100.0;  // 1.5
+		const int integer_ui_scale = full_percent / 100;  // 1
+		const double correction = system_scale / static_cast<double>(integer_ui_scale);
+
+		REQUIRE(system_scale == 1.5);
+		REQUIRE(integer_ui_scale == 1);
+		REQUIRE(correction == 1.5);
+
+		// Test window scaling: 800x600 base should become 1200x900
+		const int base_w = 800;
+		const int base_h = 600;
+		const int scaled_w = static_cast<int>(std::lround(base_w * correction));
+		const int scaled_h = static_cast<int>(std::lround(base_h * correction));
+
+		REQUIRE(scaled_w == 1200);
+		REQUIRE(scaled_h == 900);
+	}
+
+	SECTION("175% scaling (fractional)")
+	{
+		const int full_percent = 175;
+		const double system_scale = static_cast<double>(full_percent) / 100.0;  // 1.75
+		const int integer_ui_scale = full_percent / 100;  // 1
+		const double correction = system_scale / static_cast<double>(integer_ui_scale);
+
+		REQUIRE(system_scale == 1.75);
+		REQUIRE(integer_ui_scale == 1);
+		REQUIRE(correction == 1.75);
+
+		// Test window scaling: 800x600 base should become 1400x1050
+		const int base_w = 800;
+		const int base_h = 600;
+		const int scaled_w = static_cast<int>(std::lround(base_w * correction));
+		const int scaled_h = static_cast<int>(std::lround(base_h * correction));
+
+		REQUIRE(scaled_w == 1400);
+		REQUIRE(scaled_h == 1050);
+	}
+
+	SECTION("250% scaling (fractional) - Critical test case")
+	{
+		// This is the case that was broken before the fix
+		const int full_percent = 250;
+		const double system_scale = static_cast<double>(full_percent) / 100.0;  // 2.5
+		const int integer_ui_scale = full_percent / 100;  // 2
+		const double correction = system_scale / static_cast<double>(integer_ui_scale);
+
+		REQUIRE(system_scale == 2.5);
+		REQUIRE(integer_ui_scale == 2);
+		REQUIRE(correction == 1.25);  // NOT 1.5 (the old broken behavior)
+
+		// Test window scaling: GTK already applies 2x, we need to apply 1.25x more
+		// For a base of 800x600, GTK makes it 1600x1200, we should scale to 2000x1500
+		const int gtk_scaled_w = 1600;  // After GTK's 2x integer scaling
+		const int gtk_scaled_h = 1200;
+		const int final_w = static_cast<int>(std::lround(gtk_scaled_w * correction));
+		const int final_h = static_cast<int>(std::lround(gtk_scaled_h * correction));
+
+		REQUIRE(final_w == 2000);  // 2.5x total = 800 * 2.5
+		REQUIRE(final_h == 1500);  // 2.5x total = 600 * 2.5
+	}
+
+	SECTION("225% scaling (fractional)")
+	{
+		const int full_percent = 225;
+		const double system_scale = static_cast<double>(full_percent) / 100.0;  // 2.25
+		const int integer_ui_scale = full_percent / 100;  // 2
+		const double correction = system_scale / static_cast<double>(integer_ui_scale);
+
+		REQUIRE(system_scale == 2.25);
+		REQUIRE(integer_ui_scale == 2);
+		REQUIRE(correction == 1.125);
+
+		// Test window scaling: 800x600 at 2x GTK = 1600x1200, with correction = 1800x1350
+		const int gtk_scaled_w = 1600;
+		const int gtk_scaled_h = 1200;
+		const int final_w = static_cast<int>(std::lround(gtk_scaled_w * correction));
+		const int final_h = static_cast<int>(std::lround(gtk_scaled_h * correction));
+
+		REQUIRE(final_w == 1800);
+		REQUIRE(final_h == 1350);
+	}
+
+	SECTION("100% scaling (integer, no fractional)")
+	{
+		// Should not trigger fractional scaling at all (full_percent would be 0)
+		const int full_percent = 100;
+		const int integer_scale_percent = (full_percent / 100) * 100;
+
+		REQUIRE(full_percent == integer_scale_percent);  // No fractional component
+	}
+
+	SECTION("200% scaling (integer, no fractional)")
+	{
+		// Should not trigger fractional scaling at all (full_percent would be 0)
+		const int full_percent = 200;
+		const int integer_scale_percent = (full_percent / 100) * 100;
+
+		REQUIRE(full_percent == integer_scale_percent);  // No fractional component
+	}
+}
+
+
+/// Test the DPI detection logic
+TEST_CASE("DPIDetectionLogic", "[gui][scaling][dpi]")
+{
+	SECTION("Detect 125% scaling from DPI")
+	{
+		const int h_ppi = 120;  // 120 DPI
+		const double scale = static_cast<double>(h_ppi) / 96.0;
+		const int full_scale_percent = static_cast<int>(std::lround(scale * 100.0));
+		const int integer_scale_percent = (full_scale_percent / 100) * 100;
+
+		REQUIRE(full_scale_percent == 125);
+		REQUIRE(integer_scale_percent == 100);
+		REQUIRE(full_scale_percent != integer_scale_percent);  // Fractional scaling detected
+	}
+
+	SECTION("Detect 150% scaling from DPI")
+	{
+		const int h_ppi = 144;  // 144 DPI
+		const double scale = static_cast<double>(h_ppi) / 96.0;
+		const int full_scale_percent = static_cast<int>(std::lround(scale * 100.0));
+		const int integer_scale_percent = (full_scale_percent / 100) * 100;
+
+		REQUIRE(full_scale_percent == 150);
+		REQUIRE(integer_scale_percent == 100);
+		REQUIRE(full_scale_percent != integer_scale_percent);  // Fractional scaling detected
+	}
+
+	SECTION("Detect 250% scaling from DPI")
+	{
+		const int h_ppi = 240;  // 240 DPI
+		const double scale = static_cast<double>(h_ppi) / 96.0;
+		const int full_scale_percent = static_cast<int>(std::lround(scale * 100.0));
+		const int integer_scale_percent = (full_scale_percent / 100) * 100;
+
+		REQUIRE(full_scale_percent == 250);
+		REQUIRE(integer_scale_percent == 200);
+		REQUIRE(full_scale_percent != integer_scale_percent);  // Fractional scaling detected
+	}
+
+	SECTION("No fractional scaling at 100% (96 DPI)")
+	{
+		const int h_ppi = 96;  // 96 DPI (standard)
+		const double scale = static_cast<double>(h_ppi) / 96.0;
+		const int full_scale_percent = static_cast<int>(std::lround(scale * 100.0));
+		const int integer_scale_percent = (full_scale_percent / 100) * 100;
+
+		REQUIRE(full_scale_percent == 100);
+		REQUIRE(integer_scale_percent == 100);
+		REQUIRE(full_scale_percent == integer_scale_percent);  // No fractional scaling
+	}
+
+	SECTION("No fractional scaling at 200% (192 DPI)")
+	{
+		const int h_ppi = 192;  // 192 DPI
+		const double scale = static_cast<double>(h_ppi) / 96.0;
+		const int full_scale_percent = static_cast<int>(std::lround(scale * 100.0));
+		const int integer_scale_percent = (full_scale_percent / 100) * 100;
+
+		REQUIRE(full_scale_percent == 200);
+		REQUIRE(integer_scale_percent == 200);
+		REQUIRE(full_scale_percent == integer_scale_percent);  // No fractional scaling
+	}
+}
+
+
+/// @}
diff --git a/src/test_all/CMakeLists.txt b/src/test_all/CMakeLists.txt
index 7568e79..36b8a47 100644
--- a/src/test_all/CMakeLists.txt
+++ b/src/test_all/CMakeLists.txt
@@ -22,6 +22,7 @@ target_link_libraries(test_all PRIVATE
 	libdebug
 	applib_tests
 	hz_tests
+	gui_tests
 	Catch2
 )