diff --git a/.changeset/blockfrost-nullable-params.md b/.changeset/blockfrost-nullable-params.md
new file mode 100644
index 00000000..1a535b79
--- /dev/null
+++ b/.changeset/blockfrost-nullable-params.md
@@ -0,0 +1,5 @@
+---
+"@evolution-sdk/evolution": patch
+---
+
+Blockfrost protocol parameters now accept `null` for the 15 fields the Blockfrost OpenAPI spec marks nullable (`max_val_size`, `cost_models`, `cost_models_raw`, `price_mem`, `price_step`, `max_tx_ex_mem`, `max_tx_ex_steps`, `max_block_ex_mem`, `max_block_ex_steps`, `collateral_percent`, `max_collateral_inputs`, `coins_per_utxo_size`, `min_fee_ref_script_cost_per_byte`, `drep_deposit`, `gov_action_deposit`). Previously one `null` failed the whole `getProtocolParameters` decode; the decoded `null` now reaches the transform, whose existing defaults apply.
diff --git a/packages/evolution/src/sdk/provider/internal/Blockfrost.ts b/packages/evolution/src/sdk/provider/internal/Blockfrost.ts
index aca84b5f..190c4c3e 100644
--- a/packages/evolution/src/sdk/provider/internal/Blockfrost.ts
+++ b/packages/evolution/src/sdk/provider/internal/Blockfrost.ts
@@ -27,28 +27,33 @@ export const BlockfrostProtocolParameters = Schema.Struct({
   key_deposit: Schema.BigInt,
   min_utxo: Schema.optional(Schema.BigInt),
   max_tx_size: Schema.BigInt,
-  max_val_size: Schema.optional(Schema.BigInt),
+  // The Blockfrost OpenAPI spec marks the fields below nullable: a `null` must
+  // decode (to null) instead of failing the whole response; the transform's
+  // `?? 0n` / `|| 0` defaults then apply.
+  max_val_size: Schema.optionalWith(Schema.BigInt, { nullable: true }),
   utxo_cost_per_word: Schema.optional(Schema.BigInt),
-  cost_models: Schema.optional(
-    Schema.Record({ key: Schema.String, value: Schema.Record({ key: Schema.String, value: Schema.BigInt }) })
+  cost_models: Schema.optionalWith(
+    Schema.Record({ key: Schema.String, value: Schema.Record({ key: Schema.String, value: Schema.BigInt }) }),
+    { nullable: true }
   ),
-  cost_models_raw: Schema.optional(
-    Schema.Record({ key: Schema.String, value: Schema.Array(Schema.BigInt) })
+  cost_models_raw: Schema.optionalWith(
+    Schema.Record({ key: Schema.String, value: Schema.Array(Schema.BigInt) }),
+    { nullable: true }
   ),
-  price_mem: Schema.optional(Schema.NumberFromString),
-  price_step: Schema.optional(Schema.NumberFromString),
-  max_tx_ex_mem: Schema.optional(Schema.BigInt),
-  max_tx_ex_steps: Schema.optional(Schema.BigInt),
-  max_block_ex_mem: Schema.optional(Schema.BigInt),
-  max_block_ex_steps: Schema.optional(Schema.BigInt),
+  price_mem: Schema.optionalWith(Schema.NumberFromString, { nullable: true }),
+  price_step: Schema.optionalWith(Schema.NumberFromString, { nullable: true }),
+  max_tx_ex_mem: Schema.optionalWith(Schema.BigInt, { nullable: true }),
+  max_tx_ex_steps: Schema.optionalWith(Schema.BigInt, { nullable: true }),
+  max_block_ex_mem: Schema.optionalWith(Schema.BigInt, { nullable: true }),
+  max_block_ex_steps: Schema.optionalWith(Schema.BigInt, { nullable: true }),
   max_block_size: Schema.BigInt,
-  collateral_percent: Schema.optional(Schema.BigInt),
-  max_collateral_inputs: Schema.optional(Schema.BigInt),
-  coins_per_utxo_size: Schema.optional(Schema.BigInt),
-  min_fee_ref_script_cost_per_byte: Schema.optional(Schema.NumberFromString),
+  collateral_percent: Schema.optionalWith(Schema.BigInt, { nullable: true }),
+  max_collateral_inputs: Schema.optionalWith(Schema.BigInt, { nullable: true }),
+  coins_per_utxo_size: Schema.optionalWith(Schema.BigInt, { nullable: true }),
+  min_fee_ref_script_cost_per_byte: Schema.optionalWith(Schema.NumberFromString, { nullable: true }),
   // Conway era governance parameters
-  drep_deposit: Schema.optional(Schema.BigInt),
-  gov_action_deposit: Schema.optional(Schema.BigInt)
+  drep_deposit: Schema.optionalWith(Schema.BigInt, { nullable: true }),
+  gov_action_deposit: Schema.optionalWith(Schema.BigInt, { nullable: true })
 })
 
 export type BlockfrostProtocolParameters = Schema.Schema.Type<typeof BlockfrostProtocolParameters>
diff --git a/packages/evolution/test/provider/Blockfrost.test.ts b/packages/evolution/test/provider/Blockfrost.test.ts
index 0ea0ae96..93aece8d 100644
--- a/packages/evolution/test/provider/Blockfrost.test.ts
+++ b/packages/evolution/test/provider/Blockfrost.test.ts
@@ -171,6 +171,46 @@ describe("Blockfrost getProtocolParameters", () => {
     })
   })
 
+  it("accepts null for every nullable protocol parameter and falls back to the defaults", async () => {
+    // The OpenAPI spec marks these 15 fields nullable; one null must not fail the decode
+    const payload = JSON.parse(PROTOCOL_PARAMETERS) as Record<string, unknown>
+    for (const field of [
+      "max_val_size",
+      "cost_models",
+      "cost_models_raw",
+      "price_mem",
+      "price_step",
+      "max_tx_ex_mem",
+      "max_tx_ex_steps",
+      "max_block_ex_mem",
+      "max_block_ex_steps",
+      "collateral_percent",
+      "max_collateral_inputs",
+      "coins_per_utxo_size",
+      "min_fee_ref_script_cost_per_byte",
+      "drep_deposit",
+      "gov_action_deposit"
+    ]) {
+      payload[field] = null
+    }
+    stubRoutes({ "/epochs/latest/parameters": JSON.stringify(payload) })
+
+    const params = await Effect.runPromise(BlockfrostEffect.getProtocolParameters(BASE, PROJECT_ID))
+
+    expect(params.maxValSize).toBe(0)
+    expect(params.priceMem).toBe(0)
+    expect(params.priceStep).toBe(0)
+    expect(params.maxTxExMem).toBe(0n)
+    expect(params.maxTxExSteps).toBe(0n)
+    expect(params.coinsPerUtxoByte).toBe(0n)
+    expect(params.collateralPercentage).toBe(0)
+    expect(params.maxCollateralInputs).toBe(0)
+    expect(params.minFeeRefScriptCostPerByte).toBe(0)
+    expect(params.drepDeposit).toBe(0n)
+    expect(params.govActionDeposit).toBe(0n)
+    expect(params.costModels).toEqual({ PlutusV1: {}, PlutusV2: {}, PlutusV3: {} })
+  })
+
   it("falls back to the named cost models as numbers", async () => {
     stubRoutes({ "/epochs/latest/parameters": PROTOCOL_PARAMETERS.replace(/"cost_models_raw": \{[^}]*\},/, "") })