diff --git a/core/input/mouse.cpp b/core/input/mouse.cpp
index b40518d613..d6773a68a8 100644
--- a/core/input/mouse.cpp
+++ b/core/input/mouse.cpp
@@ -146,6 +146,10 @@ void SetRelativeMousePosition(float xrel, float yrel, u32 mouseId)
 {
 	if (mouseId >= std::size(mo_x_delta))
 		return;
+	// Relative motion has a different coordinate space. Rebase the next absolute
+	// position instead of replaying movement since the last absolute event.
+	mo_x_prev[mouseId] = -1;
+	mo_y_prev[mouseId] = -1;
 	int width = mo_width;
 	int height = mo_height;
 	if (config::Rotate90)
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 76157ba510..dd70aed2ce 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -27,6 +27,7 @@ target_sources(${PROJECT_NAME} PRIVATE
         src/input/ButtonComboTest.cpp
         src/input/GamepadInputHandlingTest.cpp
         src/input/MultiBindMappingTest.cpp
+        src/input/MouseTest.cpp
         src/input/InputDefTest.cpp
         src/input/InputMappingConfigFileTest.cpp
         src/input/InputSetTest.cpp
diff --git a/tests/src/input/MouseTest.cpp b/tests/src/input/MouseTest.cpp
new file mode 100644
index 0000000000..8c5e0c8e29
--- /dev/null
+++ b/tests/src/input/MouseTest.cpp
@@ -0,0 +1,139 @@
+#include "gtest/gtest.h"
+
+#include "cfg/option.h"
+#include "input/mouse.h"
+
+class MouseTest : public ::testing::Test
+{
+protected:
+    int sensitivity;
+    int stretching;
+    bool rotate;
+
+    void SetUp() override
+    {
+        sensitivity = config::MouseSensitivity;
+        stretching = config::ScreenStretching;
+        rotate = config::Rotate90;
+        config::MouseSensitivity = 100;
+        config::ScreenStretching = 100;
+        config::Rotate90 = false;
+        // Initialize the window dimensions used by relative input.
+        SetMousePosition(0, 0, 640, 480);
+        resetMouseState();
+    }
+
+    void TearDown() override
+    {
+        resetMouseState();
+        config::MouseSensitivity = sensitivity;
+        config::ScreenStretching = stretching;
+        config::Rotate90 = rotate;
+    }
+
+    static void resetMouseState()
+    {
+        for (unsigned port = 0; port < 4; port++)
+        {
+            mo_x_abs[port] = mo_y_abs[port] = 0;
+            mo_x_prev[port] = mo_y_prev[port] = -1;
+            mo_x_delta[port] = mo_y_delta[port] = mo_wheel_delta[port] = 0;
+        }
+    }
+};
+
+TEST_F(MouseTest, AbsoluteMotionUsesWindowScaleAndSensitivity)
+{
+    config::MouseSensitivity = 125;
+    SetMousePosition(200, 160, 1280, 960);
+    EXPECT_EQ(mo_x_abs[0], 100);
+    EXPECT_EQ(mo_y_abs[0], 80);
+    EXPECT_FLOAT_EQ(mo_x_delta[0], 0);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], 0);
+
+    SetMousePosition(206, 156, 1280, 960);
+    SetMousePosition(202, 158, 1280, 960);
+    EXPECT_EQ(mo_x_abs[0], 101);
+    EXPECT_EQ(mo_y_abs[0], 79);
+    EXPECT_FLOAT_EQ(mo_x_delta[0], 1.25f);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], -1.25f);
+}
+
+TEST_F(MouseTest, RelativeMotionAccumulatesAndUpdatesAbsolutePosition)
+{
+    SetMousePosition(100, 100, 640, 480);
+    config::MouseSensitivity = 50;
+    SetRelativeMousePosition(8, -4);
+    SetRelativeMousePosition(-2, 6);
+    EXPECT_FLOAT_EQ(mo_x_delta[0], 3);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], 1);
+    EXPECT_EQ(mo_x_abs[0], 103);
+    EXPECT_EQ(mo_y_abs[0], 101);
+}
+
+TEST_F(MouseTest, ReturningToAbsoluteInputDoesNotReplayConsumedMotion)
+{
+    SetMousePosition(100, 100, 640, 480);
+    SetRelativeMousePosition(100, 40);
+    // The guest has already consumed the captured movement.
+    mo_x_delta[0] = mo_y_delta[0] = 0;
+
+    SetMousePosition(200, 140, 640, 480);
+    EXPECT_FLOAT_EQ(mo_x_delta[0], 0);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], 0);
+    SetMousePosition(201, 138, 640, 480);
+    EXPECT_FLOAT_EQ(mo_x_delta[0], 1);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], -2);
+}
+
+TEST_F(MouseTest, ReturningToAbsoluteInputPreservesPendingFractions)
+{
+    SetMousePosition(100, 100, 640, 480);
+    config::MouseSensitivity = 25;
+    SetRelativeMousePosition(1, -3);
+    mo_wheel_delta[0] = 0.5f;
+
+    // A restored host position need not match the emulated absolute position.
+    SetMousePosition(300, 200, 640, 480);
+    EXPECT_EQ(mo_x_abs[0], 300);
+    EXPECT_EQ(mo_y_abs[0], 200);
+    EXPECT_FLOAT_EQ(mo_x_delta[0], 0.25f);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], -0.75f);
+    SetMousePosition(302, 204, 640, 480);
+    EXPECT_FLOAT_EQ(mo_x_delta[0], 0.75f);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], 0.25f);
+    EXPECT_FLOAT_EQ(mo_wheel_delta[0], 0.5f);
+}
+
+TEST_F(MouseTest, ChangingInputModeOnlyRebasesItsOwnPort)
+{
+    SetMousePosition(100, 100, 640, 480, 0);
+    SetMousePosition(200, 200, 640, 480, 1);
+    SetRelativeMousePosition(20, -10, 0);
+    SetMousePosition(203, 204, 640, 480, 1);
+    SetMousePosition(120, 90, 640, 480, 0);
+
+    EXPECT_FLOAT_EQ(mo_x_delta[0], 20);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], -10);
+    EXPECT_FLOAT_EQ(mo_x_delta[1], 3);
+    EXPECT_FLOAT_EQ(mo_y_delta[1], 4);
+}
+
+TEST_F(MouseTest, ReturningToAbsoluteInputPreservesRotation)
+{
+    config::Rotate90 = true;
+    SetMousePosition(100, 200, 480, 640);
+    SetRelativeMousePosition(8, 4);
+    EXPECT_FLOAT_EQ(mo_x_delta[0], -4);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], 8);
+    EXPECT_EQ(mo_x_abs[0], 435);
+    EXPECT_EQ(mo_y_abs[0], 108);
+    mo_x_delta[0] = mo_y_delta[0] = 0;
+
+    SetMousePosition(108, 204, 480, 640);
+    EXPECT_FLOAT_EQ(mo_x_delta[0], 0);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], 0);
+    SetMousePosition(110, 207, 480, 640);
+    EXPECT_FLOAT_EQ(mo_x_delta[0], -3);
+    EXPECT_FLOAT_EQ(mo_y_delta[0], 2);
+}