diff --git a/src/nouveau/compiler/nak.h b/src/nouveau/compiler/nak.h
index 937bf891e40..15035214187 100644
--- a/src/nouveau/compiler/nak.h
+++ b/src/nouveau/compiler/nak.h
@@ -41,8 +41,7 @@ struct nak_fs_key {
     * VkPipelineMultisampleStateCreateInfo::minSampleShading
     */
    bool force_sample_shading;
-
-   uint8_t _pad;
+   bool uses_underestimate;
 
    /**
     * The constant buffer index and offset at which the sample locations table lives.
diff --git a/src/nouveau/compiler/nak/sph.rs b/src/nouveau/compiler/nak/sph.rs
index cbfd45eac09..c7e0f2f9793 100644
--- a/src/nouveau/compiler/nak/sph.rs
+++ b/src/nouveau/compiler/nak/sph.rs
@@ -453,12 +453,11 @@ impl ShaderProgramHeader {
         self.set_bit(610, does_interlock);
     }
 
-    // TODO: This seems always set on fragment shaders, figure out what this is for.
     #[inline]
     #[allow(dead_code)]
-    pub fn set_unknown_bit611(&mut self, value: bool) {
+    pub fn set_uses_underestimate(&mut self, uses_underestimate: bool) {
         assert!(self.shader_type == ShaderType::Fragment);
-        self.set_bit(611, value);
+        self.set_bit(611, uses_underestimate);
     }
 
     #[inline]
@@ -533,6 +532,8 @@ pub fn encode_header(
             }
 
             let zs_self_dep = fs_key.map_or(false, |key| key.zs_self_dep);
+            let uses_underestimate =
+                fs_key.map_or(false, |key| key.uses_underestimate);
 
             // This isn't so much a "Do we write multiple render targets?" bit
             // as a "Should color0 be broadcast to all render targets?" bit. In
@@ -547,6 +548,7 @@ pub fn encode_header(
             sph.set_omap_depth(io.writes_depth);
             sph.set_omap_targets(io.writes_color);
             sph.set_does_interlock(io.does_interlock);
+            sph.set_uses_underestimate(uses_underestimate);
 
             for (index, value) in io.barycentric_attr_in.iter().enumerate() {
                 sph.set_pervertex_imap_vector(index, *value);
diff --git a/src/nouveau/vulkan/nvk_physical_device.c b/src/nouveau/vulkan/nvk_physical_device.c
index 359fffd09d2..c9cec88c629 100644
--- a/src/nouveau/vulkan/nvk_physical_device.c
+++ b/src/nouveau/vulkan/nvk_physical_device.c
@@ -873,7 +873,7 @@ nvk_get_device_properties(const struct nvk_instance *instance,
       .primitiveOverestimationSize = info->cls_eng3d >= VOLTA_A ? 1.0f / 512.0f : 0.0,
       .maxExtraPrimitiveOverestimationSize = 0.75,
       .extraPrimitiveOverestimationSizeGranularity = 0.25,
-      .primitiveUnderestimation = false,
+      .primitiveUnderestimation = info->cls_eng3d >= VOLTA_A,
       .conservativePointAndLineRasterization = true,
       .degenerateLinesRasterized = info->cls_eng3d >= VOLTA_A,
       .degenerateTrianglesRasterized = info->cls_eng3d >= PASCAL_A,
diff --git a/src/nouveau/vulkan/nvk_shader.c b/src/nouveau/vulkan/nvk_shader.c
index 4f9594e2a64..74b64dd166c 100644
--- a/src/nouveau/vulkan/nvk_shader.c
+++ b/src/nouveau/vulkan/nvk_shader.c
@@ -154,6 +154,11 @@ nvk_populate_fs_key(struct nak_fs_key *key,
    key->sample_locations_cb = 0;
    key->sample_locations_offset = nvk_root_descriptor_offset(draw.sample_locations);
 
+   /* Turn underestimate on when no state is availaible or if explicitly set */
+   if (state == NULL || state->rs == NULL ||
+       state->rs->conservative_mode == VK_CONSERVATIVE_RASTERIZATION_MODE_UNDERESTIMATE_EXT)
+      key->uses_underestimate = true;
+
    if (state == NULL)
       return;