diff --git a/src/io/sb3/interfaces.ts b/src/io/sb3/interfaces.ts
index 0a0c8fca..ba123044 100644
--- a/src/io/sb3/interfaces.ts
+++ b/src/io/sb3/interfaces.ts
@@ -331,14 +331,7 @@ export type BlockInputValue = Readonly<
 // (which could imply special handling for the other INPUT_BLOCK_* values,
 // when none such is required and whose values are never specified in this
 // mapping).
-export const inputPrimitiveOrShadowMap: {
-  // Custom procedure blocks should be serialized separately from how normal
-  // blocks are, since most of their data is stored on a "mutation" field not
-  // accounted for here.
-  [opcode in Exclude<KnownBlock["opcode"], ProcedureBlock["opcode"]>]: {
-    [fieldName: string]: number | OpCode;
-  };
-} = {
+export const inputPrimitiveOrShadowMap = {
   [OpCode.motion_movesteps]: { STEPS: BIS.MATH_NUM_PRIMITIVE },
   [OpCode.motion_turnright]: { DEGREES: BIS.MATH_NUM_PRIMITIVE },
   [OpCode.motion_turnleft]: { DEGREES: BIS.MATH_NUM_PRIMITIVE },
@@ -524,4 +517,11 @@ export const inputPrimitiveOrShadowMap: {
   [OpCode.data_hidelist]: {},
   [OpCode.argument_reporter_boolean]: {},
   [OpCode.argument_reporter_string_number]: {}
+} as const satisfies {
+  // Custom procedure blocks should be serialized separately from how normal
+  // blocks are, since most of their data is stored on a "mutation" field not
+  // accounted for here.
+  [opcode in Exclude<KnownBlock["opcode"], ProcedureBlock["opcode"]>]: {
+    [fieldName: string]: number | OpCode;
+  };
 };
diff --git a/src/io/sb3/toSb3.ts b/src/io/sb3/toSb3.ts
index 5f38f31d..bfcc78bb 100644
--- a/src/io/sb3/toSb3.ts
+++ b/src/io/sb3/toSb3.ts
@@ -4,7 +4,6 @@ import Target, { Sprite, Stage } from "../../Target";
 import * as BlockInput from "../../BlockInput";
 import * as sb3 from "./interfaces";
 import { OpCode } from "../../OpCode";
-import { prop } from "../../util/ts-util";
 
 const BIS = sb3.BlockInputStatus;
 
@@ -506,13 +505,10 @@ export default function toSb3(project: Project, options: Partial<ToSb3Options> =
           for (const arg of args) {
             const shadowId = arg.id + "-prototype-shadow";
             blockData[shadowId] = {
-              opcode: prop(
-                {
-                  boolean: OpCode.argument_reporter_boolean,
-                  numberOrString: OpCode.argument_reporter_string_number
-                },
-                arg.type
-              ),
+              opcode: {
+                boolean: OpCode.argument_reporter_boolean,
+                numberOrString: OpCode.argument_reporter_string_number
+              }[arg.type],
 
               next: null,
               parent: prototypeId,
@@ -617,7 +613,7 @@ export default function toSb3(project: Project, options: Partial<ToSb3Options> =
         }
 
         default: {
-          const inputEntries = prop(sb3.inputPrimitiveOrShadowMap, block.opcode);
+          const inputEntries = sb3.inputPrimitiveOrShadowMap[block.opcode];
 
           const initialValues: Record<string, Readonly<BlockInput.Any["value"]>> = {};
           for (const key of Object.keys(inputEntries)) {
@@ -843,13 +839,10 @@ export default function toSb3(project: Project, options: Partial<ToSb3Options> =
           id,
           name,
           type,
-          default: prop(
-            {
-              boolean: "false",
-              numberOrString: ""
-            },
-            type
-          )
+          default: {
+            boolean: "false",
+            numberOrString: ""
+          }[type]
         });
       }
 
diff --git a/src/util/ts-util.ts b/src/util/ts-util.ts
deleted file mode 100644
index e0bd5873..00000000
--- a/src/util/ts-util.ts
+++ /dev/null
@@ -1,11 +0,0 @@
-// General-purpose utility functions for TypeScript
-
-// Gets a property from an object, asserting that the property exists within
-// that object. Useful for cases where an undefined property should error,
-// since those cases will be caught at compile rather than runtime.
-//
-// From:
-// https://mariusschulz.com/blog/keyof-and-lookup-types-in-typescript
-export function prop<T, K extends keyof T>(obj: T, key: K): T[K] {
-  return obj[key];
-}