diff --git a/hw/xbox/nv2a.c b/hw/xbox/nv2a.c
index 726c4fc149..4277262b1f 100644
--- a/hw/xbox/nv2a.c
+++ b/hw/xbox/nv2a.c
@@ -2002,6 +2002,22 @@ static GraphicsObject* lookup_graphics_object(PGRAPHState *s,
     return NULL;
 }
 
+/* 16 bit to [0.0, F16_MAX = 511.9375] */
+static float convert_f16_to_float(uint16_t f16) {
+    if (f16 == 0x0000) { return 0.0; }
+    uint32_t i = (f16 << 11) + 0x3C000000;
+    return *(float*)&i;
+}
+
+/* 24 bit to [0.0, F24_MAX] */
+static float convert_f24_to_float(uint32_t f24) {
+    assert(!(f24 >> 24));
+    f24 &= 0xFFFFFF;
+    if (f24 == 0x000000) { return 0.0; }
+    uint32_t i = f24 << 7;
+    return *(float*)&i;
+}
+
 static void pgraph_update_memory_buffer(NV2AState *d, hwaddr addr, hwaddr size,
                                         bool f)
 {
@@ -5700,18 +5716,39 @@ static void pgraph_method(NV2AState *d,
             uint32_t clear_zstencil =
                 d->pgraph.regs[NV_PGRAPH_ZSTENCILCLEARVALUE];
             GLint gl_clear_stencil;
-            GLdouble gl_clear_depth;
+            GLfloat gl_clear_depth;
+
+            /* FIXME: Put these in some lookup table */
+            const float f16_max = 511.9375f;
+            /* FIXME: 7 bits of mantissa unused. maybe use full buffer? */
+            const float f24_max = 3.4027977E38;
+
             switch(pg->surface_shape.zeta_format) {
-                case NV097_SET_SURFACE_FORMAT_ZETA_Z16:
-                    /* FIXME: Remove bit for stencil clear? */
-                    gl_clear_depth = (clear_zstencil & 0xFFFF) / (double)0xFFFF;
-                    break;
-                case NV097_SET_SURFACE_FORMAT_ZETA_Z24S8:
-                    gl_clear_stencil = clear_zstencil & 0xFF;
-                    gl_clear_depth = (clear_zstencil >> 8) / (double)0xFFFFFF;
-                    break;
-                default:
-                    assert(0);
+            case NV097_SET_SURFACE_FORMAT_ZETA_Z16: {
+                uint16_t z = clear_zstencil & 0xFFFF;
+                /* FIXME: Remove bit for stencil clear? */
+                if (pg->surface_shape.z_format) {
+                    gl_clear_depth = convert_f16_to_float(z) / f16_max;
+                    assert(false); /* FIXME: Untested */
+                } else {
+                    gl_clear_depth = z / (float)0xFFFF;
+                }
+                break;
+            }
+            case NV097_SET_SURFACE_FORMAT_ZETA_Z24S8: {
+                gl_clear_stencil = clear_zstencil & 0xFF;
+                uint32_t z = clear_zstencil >> 8;
+                if (pg->surface_shape.z_format) {
+                    gl_clear_depth = convert_f24_to_float(z) / f24_max;
+                    assert(false); /* FIXME: Untested */
+                } else {
+                    gl_clear_depth = z / (float)0xFFFFFF;
+                }
+                break;
+            }
+            default:
+                assert(false);
+                break;
             }
             if (parameter & NV097_CLEAR_SURFACE_Z) {
                 gl_mask |= GL_DEPTH_BUFFER_BIT;