diff --git a/packages/server/lib/util/validation.js b/packages/server/lib/util/validation.js
index 72f25304797d..1e4e2736b0da 100644
--- a/packages/server/lib/util/validation.js
+++ b/packages/server/lib/util/validation.js
@@ -104,18 +104,19 @@ const isValidBrowserList = (key, browsers) => {
 }
 
 const isValidRetriesConfig = (key, value) => {
-  const isNullOrNumber = isOneOf([_.isNumber, _.isNull])
-
-  if (
-    isNullOrNumber(value)
-    || (_.isEqual(_.keys(value), ['runMode', 'openMode']))
-      && isNullOrNumber(value.runMode)
-      && isNullOrNumber(value.openMode)
-  ) {
+  const optionalKeys = ['runMode', 'openMode']
+  const isValidRetryValue = (val) => _.isNull(val) || (Number.isInteger(val) && val >= 0)
+  const optionalKeysAreValid = (val, k) => optionalKeys.includes(k) && isValidRetryValue(val)
+
+  if (isValidRetryValue(value)) {
+    return true
+  }
+
+  if (_.isObject(value) && _.every(value, optionalKeysAreValid)) {
     return true
   }
 
-  return errMsg(key, value, 'a number or null or an object with keys "openMode" and "runMode" with values of numbers or nulls')
+  return errMsg(key, value, 'a positive number or null or an object with keys "openMode" and "runMode" with values of numbers or nulls')
 }
 
 const isValidFirefoxGcInterval = (key, value) => {
diff --git a/packages/server/test/unit/config_spec.js b/packages/server/test/unit/config_spec.js
index 941bbdf75417..58bf50345bbb 100644
--- a/packages/server/test/unit/config_spec.js
+++ b/packages/server/test/unit/config_spec.js
@@ -690,6 +690,34 @@ describe('lib/config', () => {
         })
       })
 
+      context('retries', () => {
+        const retriesError = 'a positive number or null or an object with keys "openMode" and "runMode" with values of numbers or nulls'
+
+        // need to keep the const here or it'll get stripped by the build
+        // eslint-disable-next-line no-unused-vars
+        const cases = [
+          [{ retries: null }, 'with null', true],
+          [{ retries: 3 }, 'when a number', true],
+          [{ retries: 3.2 }, 'when a float', false],
+          [{ retries: -1 }, 'with a negative number', false],
+          [{ retries: true }, 'when true', false],
+          [{ retries: false }, 'when false', false],
+          [{ retries: {} }, 'with an empty object', true],
+          [{ retries: { runMode: 3 } }, 'when runMode is a positive number', true],
+          [{ retries: { runMode: -1 } }, 'when runMode is a negative number', false],
+          [{ retries: { openMode: 3 } }, 'when openMode is a positive number', true],
+          [{ retries: { openMode: -1 } }, 'when openMode is a negative number', false],
+          [{ retries: { openMode: 3, TypoRunMode: 3 } }, 'when there is an additional unknown key', false],
+          [{ retries: { openMode: 3, runMode: 3 } }, 'when both runMode and openMode are positive numbers', true],
+        ].forEach(([config, expectation, shouldPass]) => {
+          it(`${shouldPass ? 'passes' : 'fails'} ${expectation}`, function () {
+            this.setup(config)
+
+            return shouldPass ? this.expectValidationPasses() : this.expectValidationFails(retriesError)
+          })
+        })
+      })
+
       context('firefoxGcInterval', () => {
         it('passes if a number', function () {
           this.setup({ firefoxGcInterval: 1 })