diff --git a/src/thingdef/thingdef_expression.cpp b/src/thingdef/thingdef_expression.cpp
index 9625d83eea..1ab720c352 100644
--- a/src/thingdef/thingdef_expression.cpp
+++ b/src/thingdef/thingdef_expression.cpp
@@ -2189,6 +2189,7 @@ ExpEmit FxRandomPick::Emit(VMFunctionBuilder *build)
 			{
 				double val = static_cast<FxConstant *>(choices[i])->GetValue().GetFloat();
 				build->Emit(OP_PARAM, 0, REGT_FLOAT | REGT_KONST, build->GetConstantFloat(val));
+				build->ParamChange(-1);	// all params should use the same register here.
 			}
 		}
 		else
diff --git a/src/zscript/vmbuilder.h b/src/zscript/vmbuilder.h
index b8b1df848c..ee15e49cf6 100644
--- a/src/zscript/vmbuilder.h
+++ b/src/zscript/vmbuilder.h
@@ -51,6 +51,9 @@ public:
 	void FillAddressConstants(FVoidObj *konst, VM_ATAG *tags);
 	void FillStringConstants(FString *strings);
 
+	// PARAM increases ActiveParam; CALL decreases it.
+	void ParamChange(int delta);
+
 	// Track available registers.
 	RegAvailability Registers[4];
 
@@ -76,8 +79,6 @@ private:
 
 	TArray<VMOP> Code;
 
-	// PARAM increases ActiveParam; CALL decreases it.
-	void ParamChange(int delta);
 };
 
 #endif