diff --git a/hw/display/milkymist-tmu2.c b/hw/display/milkymist-tmu2.c
index 5c666f9b24..920374b985 100644
--- a/hw/display/milkymist-tmu2.c
+++ b/hw/display/milkymist-tmu2.c
@@ -257,7 +257,7 @@ static void tmu2_start(MilkymistTMU2State *s)
     glColor4f(m, m, m, (float)(s->regs[R_ALPHA] + 1) / 64.0f);
 
     /* Read the QEMU dest. framebuffer into the OpenGL framebuffer */
-    fb_len = 2 * s->regs[R_DSTHRES] * s->regs[R_DSTVRES];
+    fb_len = 2ULL * s->regs[R_DSTHRES] * s->regs[R_DSTVRES];
     fb = cpu_physical_memory_map(s->regs[R_DSTFBUF], &fb_len, 0);
     if (fb == NULL) {
         glDeleteTextures(1, &texture);