diff --git a/neo/renderer/Material.cpp b/neo/renderer/Material.cpp
index 2655a1b4..dc51e92a 100644
--- a/neo/renderer/Material.cpp
+++ b/neo/renderer/Material.cpp
@@ -1862,8 +1862,12 @@ void idMaterial::ParseDeform(idLexer& src) {
 idMaterial::GetDiffuseImage
 ===================
 */
-idImage* idMaterial::GetDiffuseImage(void) const {
+idImage* idMaterial::GetDiffuseImage(const float* regs) const {
 	for (int i = 0; i < numStages; i++) {
+		if (regs && regs[stages[i].conditionRegister] == 0) {
+			continue;
+		}
+
 		if (stages[i].lighting == SL_DIFFUSE && stages[i].texture.image) {
 			return stages[i].texture.image;
 		}
@@ -1933,9 +1937,13 @@ idImage* idMaterial::GetSpecImage(void) const {
 idMaterial::GetGlowImage
 ===================
 */
-idImage* idMaterial::GetGlowImage(void) const {
+idImage* idMaterial::GetGlowImage(const float *regs) const {
 #ifdef PREY
 	for (int i = 0; i < numStages; i++) {
+		if (regs && regs[stages[i].conditionRegister] == 0) {
+			continue;
+		}
+
 		if ((stages[i].lighting == SL_GLOWMAP  || stages[i].isGlow) && stages[i].texture.image) {
 			return stages[i].texture.image;
 		}
@@ -2784,7 +2792,6 @@ void idMaterial::AddReference() {
 		}
 	}
 }
-
 /*
 ===============
 idMaterial::EvaluateRegisters
@@ -2794,13 +2801,13 @@ then all expressions are evaluated, leaving the material registers
 set to their apropriate values.
 ===============
 */
-void idMaterial::EvaluateRegisters( float *registers, const float shaderParms[MAX_ENTITY_SHADER_PARMS],
-									const viewDef_t *view, idSoundEmitter *soundEmitter ) const {
+void idMaterial::EvaluateRegisters(float* registers, const float shaderParms[MAX_ENTITY_SHADER_PARMS],
+	const viewDef_t* view, idSoundEmitter* soundEmitter) const {
 	int		i, b;
-	expOp_t	*op;
+	expOp_t* op;
 
 	// copy the material constants
-	for ( i = EXP_REG_NUM_PREDEFINED ; i < numRegisters ; i++ ) {
+	for (i = EXP_REG_NUM_PREDEFINED; i < numRegisters; i++) {
 		registers[i] = expressionRegisters[i];
 	}
 
@@ -2818,7 +2825,15 @@ void idMaterial::EvaluateRegisters( float *registers, const float shaderParms[MA
 	registers[EXP_REG_PARM9] = shaderParms[9];
 	registers[EXP_REG_PARM10] = shaderParms[10];
 	registers[EXP_REG_PARM11] = shaderParms[11];
+
+#ifdef PREY
+	// Prey has one extra entity shader parm copied into predefined register 21.
+	// Make sure EXP_REG_GLOBAL0 is defined as the correct predefined register index.
+	registers[EXP_REG_GLOBAL0] = shaderParms[12];
+#else
 	registers[EXP_REG_GLOBAL0] = view->renderView.shaderParms[0];
+#endif
+
 	registers[EXP_REG_GLOBAL1] = view->renderView.shaderParms[1];
 	registers[EXP_REG_GLOBAL2] = view->renderView.shaderParms[2];
 	registers[EXP_REG_GLOBAL3] = view->renderView.shaderParms[3];
@@ -2828,72 +2843,98 @@ void idMaterial::EvaluateRegisters( float *registers, const float shaderParms[MA
 	registers[EXP_REG_GLOBAL7] = view->renderView.shaderParms[7];
 
 	op = ops;
-	for ( i = 0 ; i < numOps ; i++, op++ ) {
-		switch( op->opType ) {
-#ifdef PREY
-		case OP_TYPE_FRAGMENTPROGRAMS:
-			registers[op->c] = glConfig.ARBFragmentProgramAvailable;
-			break;
-#endif
+	for (i = 0; i < numOps; i++, op++) {
+		switch (op->opType) {
 		case OP_TYPE_ADD:
 			registers[op->c] = registers[op->a] + registers[op->b];
 			break;
+
 		case OP_TYPE_SUBTRACT:
 			registers[op->c] = registers[op->a] - registers[op->b];
 			break;
+
 		case OP_TYPE_MULTIPLY:
 			registers[op->c] = registers[op->a] * registers[op->b];
 			break;
+
 		case OP_TYPE_DIVIDE:
+#ifdef PREY
+			// Prey returns 0.0 when dividing by zero.
+			if (registers[op->b] == 0.0f) {
+				registers[op->c] = 0.0f;
+			}
+			else {
+				registers[op->c] = registers[op->a] / registers[op->b];
+			}
+#else
 			registers[op->c] = registers[op->a] / registers[op->b];
+#endif
 			break;
+
 		case OP_TYPE_MOD:
 			b = (int)registers[op->b];
 			b = b != 0 ? b : 1;
 			registers[op->c] = (int)registers[op->a] % b;
 			break;
+
 		case OP_TYPE_TABLE:
-			{
-				const idDeclTable *table = static_cast<const idDeclTable *>( declManager->DeclByIndex( DECL_TABLE, op->a ) );
-				registers[op->c] = table->TableLookup( registers[op->b] );
-			}
-			break;
+		{
+			const idDeclTable* table = static_cast<const idDeclTable*>(declManager->DeclByIndex(DECL_TABLE, op->a));
+			registers[op->c] = table->TableLookup(registers[op->b]);
+		}
+		break;
+
 		case OP_TYPE_SOUND:
-			if ( soundEmitter ) {
+			if (soundEmitter) {
 				registers[op->c] = soundEmitter->CurrentAmplitude();
-			} else {
+			}
+			else {
 				registers[op->c] = 0;
 			}
 			break;
+
 		case OP_TYPE_GT:
-			registers[op->c] = registers[ op->a ] > registers[op->b];
+			registers[op->c] = registers[op->a] > registers[op->b];
 			break;
+
 		case OP_TYPE_GE:
-			registers[op->c] = registers[ op->a ] >= registers[op->b];
+			registers[op->c] = registers[op->a] >= registers[op->b];
 			break;
+
 		case OP_TYPE_LT:
-			registers[op->c] = registers[ op->a ] < registers[op->b];
+			registers[op->c] = registers[op->a] < registers[op->b];
 			break;
+
 		case OP_TYPE_LE:
-			registers[op->c] = registers[ op->a ] <= registers[op->b];
+			registers[op->c] = registers[op->a] <= registers[op->b];
 			break;
+
 		case OP_TYPE_EQ:
-			registers[op->c] = registers[ op->a ] == registers[op->b];
+			registers[op->c] = registers[op->a] == registers[op->b];
 			break;
+
 		case OP_TYPE_NE:
-			registers[op->c] = registers[ op->a ] != registers[op->b];
+			registers[op->c] = registers[op->a] != registers[op->b];
 			break;
+
 		case OP_TYPE_AND:
-			registers[op->c] = registers[ op->a ] && registers[op->b];
+			registers[op->c] = registers[op->a] && registers[op->b];
 			break;
+
 		case OP_TYPE_OR:
-			registers[op->c] = registers[ op->a ] || registers[op->b];
+			registers[op->c] = registers[op->a] || registers[op->b];
 			break;
+
+#ifdef PREY
+		case OP_TYPE_FRAGMENTPROGRAMS:
+			registers[op->c] = glConfig.ARBFragmentProgramAvailable ? 1.0f : 0.0f;
+			break;
+#endif
+
 		default:
-			common->FatalError( "R_EvaluateExpression: bad opcode" );
+			common->FatalError("R_EvaluateExpression: bad opcode");
 		}
 	}
-
 }
 
 /*
diff --git a/neo/renderer/Material.h b/neo/renderer/Material.h
index ae2f5837..d9f77488 100644
--- a/neo/renderer/Material.h
+++ b/neo/renderer/Material.h
@@ -506,7 +506,7 @@ public:
 	bool				ReceivesFog(void) const { return (IsDrawn() && !noFog && coverage != MC_TRANSLUCENT); }
 // jmarshall
 	// Returns the diffuse/albedo image used by this material stage.
-	idImage* GetDiffuseImage(void) const;
+	idImage* GetDiffuseImage(const float *regs) const;
 
 	// Returns the bump/normal map image used by this material stage.
 	idImage* GetBumpImage(void) const;
@@ -515,7 +515,7 @@ public:
 	idImage* GetSpecImage(void) const;
 
 	// Returns the glow/emissive map image used by this material stage.
-	idImage* GetGlowImage(void) const;
+	idImage* GetGlowImage(const float* regs) const;
 
 	// Returns true if this material participates in dynamic lighting.
 	bool IsLitMaterial(void) const;
diff --git a/neo/renderer/draw_common.cpp b/neo/renderer/draw_common.cpp
index e119989c..a42a1d0b 100644
--- a/neo/renderer/draw_common.cpp
+++ b/neo/renderer/draw_common.cpp
@@ -534,7 +534,7 @@ void RB_T_FillDepthBuffer( const drawSurf_t *surf ) {
 		// bind the texture
 		GL_SelectTexture(0);
 		glEnable(GL_TEXTURE_2D);
-		shader->GetDiffuseImage()->Bind();
+		shader->GetDiffuseImage(regs)->Bind();
 
 		GL_SelectTexture(1);
 		glEnable(GL_TEXTURE_2D);
@@ -546,7 +546,7 @@ void RB_T_FillDepthBuffer( const drawSurf_t *surf ) {
 		shader->GetSpecImage()->Bind();
 		glBindSpecularMapTexture(shader->GetSpecImage()->texnum);
 
-		idImage* glowMapImage = shader->GetGlowImage();
+		idImage* glowMapImage = shader->GetGlowImage(regs);
 		if (glowMapImage)
 		{
 			GL_SelectTexture(3);
@@ -989,11 +989,6 @@ void RB_STD_T_RenderShaderPasses( const drawSurf_t *surf ) {
 			continue;
 		}
 
-		// check the stage enable condition
-		if (regs[pStage->conditionRegister] == 0) {
-			continue;
-		}
-
 		// select the vertex color source
 		if ( pStage->vertexColor == SVC_IGNORE ) {
 			glColor4fv( color );