diff --git a/server/package.json b/server/package.json
index f1a3e0386..fbdfee609 100644
--- a/server/package.json
+++ b/server/package.json
@@ -82,7 +82,7 @@
 		"rimraf": "3.0.2",
 		"safe-json-stringify": "1.2.0",
 		"seq-logging": "^1.1.1",
-		"tachi-common": "0.5.4",
+		"tachi-common": "0.5.5",
 		"ts-node": "10.0.0",
 		"tsconfig-paths": "3.10.1",
 		"typescript": "4.3.4",
diff --git a/server/pnpm-lock.yaml b/server/pnpm-lock.yaml
index a9a1c0ce4..ab20ddb7b 100644
--- a/server/pnpm-lock.yaml
+++ b/server/pnpm-lock.yaml
@@ -63,7 +63,7 @@ specifiers:
   safe-json-stringify: 1.2.0
   seq-logging: ^1.1.1
   supertest: 6.1.3
-  tachi-common: 0.5.4
+  tachi-common: 0.5.5
   tap: 15.0.9
   ts-node: 10.0.0
   tsconfig-paths: 3.10.1
@@ -107,7 +107,7 @@ dependencies:
   rimraf: 3.0.2
   safe-json-stringify: 1.2.0
   seq-logging: 1.1.1
-  tachi-common: 0.5.4
+  tachi-common: 0.5.5
   ts-node: 10.0.0_83f53b0a0c5616d3fa00ed4e30b9ce1b
   tsconfig-paths: 3.10.1
   typescript: 4.3.4
@@ -5386,8 +5386,8 @@ packages:
       strip-ansi: 6.0.0
     dev: true
 
-  /tachi-common/0.5.4:
-    resolution: {integrity: sha512-6QDpdvyGB2JOzPcW+7Hm/jXCKXXrIB6KgTKmvVq86771Iyali/oA2iigSb+oeVUQb8zNX2IM/s9hRD9F+80xTw==}
+  /tachi-common/0.5.5:
+    resolution: {integrity: sha512-LFKK+3xhlDQJ07yUij2/H+0cPiHXoXKdFQyR8X1ZNSjsluZoWncR9Rkqwhxlt/WeFBaGyLjkYkpdMkRYZMLVUg==}
     dependencies:
       monk: 7.3.4
     transitivePeerDependencies:
diff --git a/server/src/server/router/api/v1/users/_userID/games/_game/_playtype/settings/router.test.ts b/server/src/server/router/api/v1/users/_userID/games/_game/_playtype/settings/router.test.ts
index 6a1a1a4ce..778f29193 100644
--- a/server/src/server/router/api/v1/users/_userID/games/_game/_playtype/settings/router.test.ts
+++ b/server/src/server/router/api/v1/users/_userID/games/_game/_playtype/settings/router.test.ts
@@ -138,6 +138,114 @@ t.test("PATCH /api/v1/users/:userID/games/:game/:playtype/settings", (t) => {
 		t.end();
 	});
 
+	t.test("Should update an IIDX player's bpiTarget settings.", async (t) => {
+		t.beforeEach(async () => {
+			await db["api-tokens"].insert({
+				userID: 1,
+				identifier: "api_token",
+				permissions: {
+					customise_profile: true,
+				},
+				token: "api_token",
+				fromAPIClient: null,
+			});
+		});
+
+		const f = async (target: number) => {
+			const res = await mockApi
+				.patch("/api/v1/users/1/games/iidx/SP/settings")
+				.set("Authorization", "Bearer api_token")
+				.send({
+					gameSpecific: {
+						bpiTarget: target,
+					},
+				});
+
+			t.equal(res.statusCode, 200);
+
+			t.strictSame(
+				res.body.body,
+				{
+					userID: 1,
+					game: "iidx",
+					playtype: "SP",
+					preferences: {
+						preferredScoreAlg: null,
+						preferredSessionAlg: null,
+						preferredProfileAlg: null,
+						scoreBucket: null,
+						stats: [],
+						gameSpecific: {
+							bpiTarget: target,
+						},
+					},
+				},
+				"Should only update the mutated properties."
+			);
+
+			const data = await db["game-settings"].findOne({
+				userID: 1,
+				game: "iidx",
+				playtype: "SP",
+			});
+
+			t.equal(data?.preferences.gameSpecific.bpiTarget, target);
+		};
+
+		for (const target of [0, 10, 15, 100]) {
+			t.test(`Should be able to update the BPI target to ${target}`, async (t) => {
+				await f(target);
+
+				t.end();
+			});
+		}
+
+		t.test("Should reject float BPI targets.", async (t) => {
+			const res = await mockApi
+				.patch("/api/v1/users/1/games/iidx/SP/settings")
+				.set("Authorization", "Bearer api_token")
+				.send({
+					gameSpecific: {
+						bpiTarget: 10.5,
+					},
+				});
+
+			t.equal(res.statusCode, 400);
+		});
+
+		t.test("Should reject negative BPI targets", async (t) => {
+			const res = await mockApi
+				.patch("/api/v1/users/1/games/iidx/SP/settings")
+				.set("Authorization", "Bearer api_token")
+				.send({
+					gameSpecific: {
+						bpiTarget: -10,
+					},
+				});
+
+			t.equal(res.statusCode, 400);
+
+			t.end();
+		});
+
+		t.test("Should reject >= 100 BPI targets", async (t) => {
+			const res = await mockApi
+				.patch("/api/v1/users/1/games/iidx/SP/settings")
+				.set("Authorization", "Bearer api_token")
+				.send({
+					gameSpecific: {
+						bpiTarget: 101,
+					},
+				});
+
+			t.equal(res.statusCode, 400);
+
+			t.end();
+		});
+
+		t.end();
+	});
+
 	t.test("Should reject a arbitrary things on game specific settings.", async (t) => {
 		await db["api-tokens"].insert({
 			userID: 1,
diff --git a/server/src/server/router/api/v1/users/_userID/games/_game/_playtype/settings/router.ts b/server/src/server/router/api/v1/users/_userID/games/_game/_playtype/settings/router.ts
index 9eeddb29c..dd07f3463 100644
--- a/server/src/server/router/api/v1/users/_userID/games/_game/_playtype/settings/router.ts
+++ b/server/src/server/router/api/v1/users/_userID/games/_game/_playtype/settings/router.ts
@@ -52,14 +52,12 @@ router.patch(
 
 			if (game === "iidx") {
 				schema = {
-					display2DXTra: "boolean",
-					bpiTarget: p.isBoundedInteger(0, 100),
+					display2DXTra: p.optional("boolean"),
+					bpiTarget: p.optional(p.isBoundedInteger(0, 100)),
 				};
 			}
-			// A limitation in prudence means that validating top-level properties like this isn't
-			// possible.
-			// A prudence v1.0. should fix this!
-			const err = p({ __: req.body.gameSpecific }, { __: p.optional(schema) }, {});
+
+			const err = p(req.body.gameSpecific, schema);
 
 			if (err) {
 				return res.status(400).json({