diff --git a/code/def_files/data/effects/main-f.sdr b/code/def_files/data/effects/main-f.sdr
index 1a46b848d9e..f8390b496fc 100644
--- a/code/def_files/data/effects/main-f.sdr
+++ b/code/def_files/data/effects/main-f.sdr
@@ -229,10 +229,13 @@ vec3 CalculateLighting(vec3 normal, vec3 diffuseMaterial, vec3 specularMaterial,
 	vec3 lightSpecular = vec3(0.0, 0.0, 0.0);
 
 #ifdef MODEL_SDR_FLAG_RT_SHADOWS
-	// Whenever this compile-time flag is present we're always in Vulkan/large-shader
-	// mode, so `flags`/MODEL_SDR_FLAG_SHADOWS (the runtime shadow-receiving gate that
-	// IF_FLAG expands to elsewhere in this file) are guaranteed to exist here too.
-	bool rtShadowsActive = (flags & MODEL_SDR_FLAG_SHADOWS) != 0;
+	// Whether this material actually receives shadows. This has to go through IF_FLAG
+	// rather than testing `flags` directly: in small-shader mode MODEL_SDR_FLAG_SHADOWS
+	// is only a (valueless) preprocessor define, so it can't be used in an expression.
+	bool rtShadowsActive = false;
+	#prereplace IF_FLAG MODEL_SDR_FLAG_SHADOWS
+		rtShadowsActive = true;
+	#prereplace ENDIF_FLAG //MODEL_SDR_FLAG_SHADOWS
 	mat4 invView = inverse(viewMatrix);
 	vec3 worldPos = (invView * vertIn.position).xyz;
 	vec3 worldNormal = normalize((invView * vec4(normal, 0.0)).xyz);
diff --git a/code/def_files/data/effects/main-v.sdr b/code/def_files/data/effects/main-v.sdr
index 39426766ab1..7933ecf3578 100644
--- a/code/def_files/data/effects/main-v.sdr
+++ b/code/def_files/data/effects/main-v.sdr
@@ -128,15 +128,19 @@ layout(set = 1, binding = 3, std430) readonly buffer TransformBuffer {
 	mat4 transforms[];
 } transformBuf;
 
-// Outputs to fragment shader
+// Outputs to fragment shader. The shadow members are gated exactly like the matching
+// block in main-f.sdr so the stage interfaces stay identical in small-shader mode.
 layout(location = 0) out VertexOutput {
 	vec4 position;
 	vec3 normal;
 	vec4 texCoord;
 	mat3 tangentMatrix;
 	float fogDist;
+
+#prereplace IF_FLAG_COMPILED MODEL_SDR_FLAG_SHADOWS
 	vec4 shadowUV[NUM_SHADOW_CASCADES];
 	vec4 shadowPos;
+#prereplace ENDIF_FLAG_COMPILED MODEL_SDR_FLAG_SHADOWS
 } vertOut;
 #else
 #prereplace IF_FLAG_COMPILED MODEL_SDR_FLAG_TRANSFORM
diff --git a/code/def_files/data/effects/model_shader_flags.h b/code/def_files/data/effects/model_shader_flags.h
index 5fa94ca4b91..ed9919148f3 100644
--- a/code/def_files/data/effects/model_shader_flags.h
+++ b/code/def_files/data/effects/model_shader_flags.h
@@ -29,12 +29,12 @@ SDR_FLAG(MODEL_SDR_FLAG_ALPHA_MULT    , (1 << 14), false)
 //But since these are checked with ifdefs even for the large shader, they must never be available in GLSL mode
 SDR_FLAG(MODEL_SDR_FLAG_THICK_OUTLINES, (1 << 16), true)
 
-// Like MODEL_SDR_FLAG_SHADOW_MAP/THICK_OUTLINES above, this must stay a genuine
-// compile-time ifdef check (not the runtime flag-branch macros used for ordinary
-// MODEL_SDR_FLAG_* bits) since Vulkan always runs in "large shader" mode, where
-// those bits are only checked via a runtime `flags` uniform -- ray query usage
-// can't be gated that way, since the GL_EXT_ray_query extension and its types
-// must not appear at all in a shader compiled for hardware that doesn't support it.
+// Like MODEL_SDR_FLAG_THICK_OUTLINES above, this must stay a genuine compile-time
+// ifdef check (not the runtime flag-branch macros used for ordinary MODEL_SDR_FLAG_*
+// bits): the GL_EXT_ray_query extension and its types must not appear at all in a
+// shader compiled for hardware that doesn't support it, so the usage can't be left
+// in the code and skipped via a runtime `flags` branch the way large-shader mode
+// handles the ordinary bits.
 SDR_FLAG(MODEL_SDR_FLAG_RT_SHADOWS    , (1 << 17), true)
 
 #endif
\ No newline at end of file
diff --git a/code/graphics/vulkan/gr_vulkan.cpp b/code/graphics/vulkan/gr_vulkan.cpp
index 4d5d5768ff8..8fb01daa2a0 100644
--- a/code/graphics/vulkan/gr_vulkan.cpp
+++ b/code/graphics/vulkan/gr_vulkan.cpp
@@ -142,7 +142,10 @@ bool vulkan_is_capable(gr_capability capability)
 		// Vulkan always supports BC1/BC2/BC3 (S3TC equivalent) as core features
 		return true;
 	case gr_capability::CAPABILITY_LARGE_SHADER:
-		return true;
+		// Same troubleshooting switch as OpenGL: -no_large_shaders splits the model
+		// ubershader into per-flag-combination variants for drivers that choke on the
+		// single large program (see main_large.sdr / main_small.sdr).
+		return !Cmdline_no_large_shaders;
 	case gr_capability::CAPABILITY_INSTANCED_RENDERING:
 		return true;
 	case gr_capability::CAPABILITY_FAST_SHADOWS: