diff --git a/yarn-project/foundation/src/log/bigint-utils.ts b/yarn-project/foundation/src/log/bigint-utils.ts
new file mode 100644
index 000000000000..6cc94101ac2f
--- /dev/null
+++ b/yarn-project/foundation/src/log/bigint-utils.ts
@@ -0,0 +1,22 @@
+/**
+ * Converts bigint values to strings recursively in a log object to avoid serialization issues.
+ */
+export function convertBigintsToStrings(obj: unknown): unknown {
+  if (typeof obj === 'bigint') {
+    return String(obj);
+  }
+
+  if (Array.isArray(obj)) {
+    return obj.map(item => convertBigintsToStrings(item));
+  }
+
+  if (obj !== null && typeof obj === 'object') {
+    const result: Record<string, unknown> = {};
+    for (const key in obj) {
+      result[key] = convertBigintsToStrings((obj as Record<string, unknown>)[key]);
+    }
+    return result;
+  }
+
+  return obj;
+}
diff --git a/yarn-project/foundation/src/log/gcloud-logger-config.ts b/yarn-project/foundation/src/log/gcloud-logger-config.ts
index db3b331141df..2e036212af71 100644
--- a/yarn-project/foundation/src/log/gcloud-logger-config.ts
+++ b/yarn-project/foundation/src/log/gcloud-logger-config.ts
@@ -1,5 +1,7 @@
 import type { pino } from 'pino';
 
+import { convertBigintsToStrings } from './bigint-utils.js';
+
 /* eslint-disable camelcase */
 
 const GOOGLE_CLOUD_TRACE_ID = 'logging.googleapis.com/trace';
@@ -15,6 +17,9 @@ export const GoogleCloudLoggerConfig = {
   messageKey: 'message',
   formatters: {
     log(object: Record<string, unknown>): Record<string, unknown> {
+      // Convert bigints to strings recursively to avoid serialization issues
+      object = convertBigintsToStrings(object) as Record<string, unknown>;
+
       // Add trace context attributes following Cloud Logging structured log format described
       // in https://cloud.google.com/logging/docs/structured-logging#special-payload-fields
       const { trace_id, span_id, trace_flags, ...rest } = object;
diff --git a/yarn-project/foundation/src/log/pino-logger.test.ts b/yarn-project/foundation/src/log/pino-logger.test.ts
index 1efdcf038f18..9881535d4f58 100644
--- a/yarn-project/foundation/src/log/pino-logger.test.ts
+++ b/yarn-project/foundation/src/log/pino-logger.test.ts
@@ -188,6 +188,91 @@ describe('pino-logger', () => {
     });
   });
 
+  it('converts bigints to strings recursively ', () => {
+    const testLogger = createLogger('bigint-test');
+    capturingStream.clear();
+
+    testLogger.info('comprehensive bigint conversion', {
+      // Top-level bigints
+      amount: 123456789012345678901234n,
+      slot: 42n,
+      // Nested objects
+      nested: {
+        value: 999999999999999999n,
+        deepNested: {
+          id: 12345678901234567890n,
+        },
+      },
+      // Arrays with bigints
+      array: [1n, 2n, 3n],
+      mixedArray: [{ id: 999n }, { id: 888n }],
+      // Mixed types
+      numberValue: 123,
+      stringValue: 'test',
+      boolValue: true,
+      nullValue: null,
+    });
+
+    const entries = capturingStream.getJsonLines();
+    expect(entries).toHaveLength(1);
+    expect(entries[0]).toMatchObject({
+      module: 'bigint-test',
+      msg: 'comprehensive bigint conversion',
+      // All bigints converted to strings
+      amount: '123456789012345678901234',
+      slot: '42',
+      nested: {
+        value: '999999999999999999',
+        deepNested: {
+          id: '12345678901234567890',
+        },
+      },
+      array: ['1', '2', '3'],
+      mixedArray: [{ id: '999' }, { id: '888' }],
+      // Other types preserved
+      numberValue: 123,
+      stringValue: 'test',
+      boolValue: true,
+      nullValue: null,
+    });
+  });
+
+  it('does not mutate the original log data object', () => {
+    const testLogger = createLogger('mutation-test');
+    capturingStream.clear();
+
+    const originalData = {
+      amount: 123456789012345678901234n,
+      nested: {
+        value: 999n,
+      },
+      array: [1n, 2n, 3n],
+    };
+
+    // Keep references to verify mutation
+    const originalAmount = originalData.amount;
+    const originalNestedValue = originalData.nested.value;
+    const originalArrayItem = originalData.array[0];
+
+    testLogger.info('mutation test', originalData);
+
+    // Verify the original object was NOT mutated
+    expect(originalData.amount).toBe(originalAmount);
+    expect(typeof originalData.amount).toBe('bigint');
+    expect(originalData.nested.value).toBe(originalNestedValue);
+    expect(typeof originalData.nested.value).toBe('bigint');
+    expect(originalData.array[0]).toBe(originalArrayItem);
+    expect(typeof originalData.array[0]).toBe('bigint');
+
+    // But the logged version should have strings
+    const entries = capturingStream.getJsonLines();
+    expect(entries[0]).toMatchObject({
+      amount: '123456789012345678901234',
+      nested: { value: '999' },
+      array: ['1', '2', '3'],
+    });
+  });
+
   it('returns bindings via getBindings', () => {
     const testLogger = createLogger('bindings-test', { actor: 'main', instanceId: 'id-123' });
     const bindings = testLogger.getBindings();
diff --git a/yarn-project/foundation/src/log/pino-logger.ts b/yarn-project/foundation/src/log/pino-logger.ts
index 2a41d44bf117..2395cc908ec0 100644
--- a/yarn-project/foundation/src/log/pino-logger.ts
+++ b/yarn-project/foundation/src/log/pino-logger.ts
@@ -7,6 +7,7 @@ import { inspect } from 'util';
 import { compactArray } from '../collection/array.js';
 import type { EnvVar } from '../config/index.js';
 import { parseBooleanEnv } from '../config/parse-env.js';
+import { convertBigintsToStrings } from './bigint-utils.js';
 import { GoogleCloudLoggerConfig } from './gcloud-logger-config.js';
 import { getLogLevelFromFilters, parseEnv } from './log-filters.js';
 import type { LogLevel } from './log-levels.js';
@@ -165,6 +166,9 @@ const pinoOpts: pino.LoggerOptions<keyof typeof customLevels> = {
       ...redactedPaths.map(p => `opts.${p}`),
     ],
   },
+  formatters: {
+    log: obj => convertBigintsToStrings(obj) as Record<string, unknown>,
+  },
   ...(useGcloudLogging ? GoogleCloudLoggerConfig : {}),
 };
 
diff --git a/yarn-project/slasher/src/slash_offenses_collector.ts b/yarn-project/slasher/src/slash_offenses_collector.ts
index 274357a97c6a..551f868ccec3 100644
--- a/yarn-project/slasher/src/slash_offenses_collector.ts
+++ b/yarn-project/slasher/src/slash_offenses_collector.ts
@@ -85,11 +85,7 @@ export class SlashOffensesCollector {
         }
       }
 
-      this.log.info(`Adding pending offense for validator ${arg.validator}`, {
-        ...pendingOffense,
-        epochOrSlot: pendingOffense.epochOrSlot.toString(),
-        amount: pendingOffense.amount.toString(),
-      });
+      this.log.info(`Adding pending offense for validator ${arg.validator}`, pendingOffense);
       await this.offensesStore.addPendingOffense(pendingOffense);
     }
   }