diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 8ba3a245547..58dd31e8c43 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -437,6 +437,12 @@ optimizations.extend([
 
    (('~flrp', a, 0.0, c), ('fadd', ('fmul', ('fneg', a), c), a)),
 
+   # D3D9 vertex shader trunc
+   (('fadd', ('ffloor', a), ('b2f', ('iand', ('flt', a, 0), ('flt', ('fneg', ('ffract', a)), ('ffract', a))))), ('ftrunc', ('fadd', a, 0))),
+   # D3D9 pixel shader trunc
+   (('fadd', ('ffloor', a), ('b2f', ('inot', ('fge', 0, ('fmin', ('fneg', a), ('ffract', a)))))), ('ftrunc', ('fadd', a, 0))),
+   (('fadd', ('ffloor', a), ('b2f', ('flt', 0, ('fmin', ('fneg', a), ('ffract', a))))), ('ftrunc', ('fadd', a, 0))),
+
    (('ftrunc@16', a), ('bcsel', ('flt', a, 0.0), ('fneg', ('ffloor', ('fabs', a))), ('ffloor', ('fabs', a))), 'options->lower_ftrunc'),
    (('ftrunc@32', a), ('bcsel', ('flt', a, 0.0), ('fneg', ('ffloor', ('fabs', a))), ('ffloor', ('fabs', a))), 'options->lower_ftrunc'),
    (('ftrunc@64', a), ('bcsel', ('flt', a, 0.0), ('fneg', ('ffloor', ('fabs', a))), ('ffloor', ('fabs', a))),