diff --git a/packages/netlify-cms-core/src/constants/__tests__/configSchema.spec.js b/packages/netlify-cms-core/src/constants/__tests__/configSchema.spec.js
index 20b7ebe7..ee2a4fb6 100644
--- a/packages/netlify-cms-core/src/constants/__tests__/configSchema.spec.js
+++ b/packages/netlify-cms-core/src/constants/__tests__/configSchema.spec.js
@@ -173,13 +173,13 @@ describe('config', () => {
 
     it('should throw if collection publish is not a boolean', () => {
       expect(() => {
-        validateConfig(merge(validConfig, { collections: [{ publish: 'false' }] }));
+        validateConfig(merge({}, validConfig, { collections: [{ publish: 'false' }] }));
       }).toThrowError("'collections[0].publish' should be boolean");
     });
 
     it('should not throw if collection publish is a boolean', () => {
       expect(() => {
-        validateConfig(merge(validConfig, { collections: [{ publish: false }] }));
+        validateConfig(merge({}, validConfig, { collections: [{ publish: false }] }));
       }).not.toThrowError();
     });
 
@@ -201,10 +201,48 @@ describe('config', () => {
       }).not.toThrow();
     });
 
+    it('should throw if collection names are not unique', () => {
+      expect(() => {
+        validateConfig(
+          merge({}, validConfig, {
+            collections: [validConfig.collections[0], validConfig.collections[0]],
+          }),
+        );
+      }).toThrowError("'collections' collections names must be unique");
+    });
+
+    it('should throw if collection file names are not unique', () => {
+      expect(() => {
+        validateConfig(
+          merge({}, validConfig, {
+            collections: [
+              {},
+              {
+                files: [
+                  {
+                    name: 'a',
+                    label: 'a',
+                    file: 'a.md',
+                    fields: [{ name: 'title', label: 'title', widget: 'string' }],
+                  },
+                  {
+                    name: 'a',
+                    label: 'b',
+                    file: 'b.md',
+                    fields: [{ name: 'title', label: 'title', widget: 'string' }],
+                  },
+                ],
+              },
+            ],
+          }),
+        );
+      }).toThrowError("'collections[1].files' files names must be unique");
+    });
+
     it('should throw if collection fields names are not unique', () => {
       expect(() => {
         validateConfig(
-          merge(validConfig, {
+          merge({}, validConfig, {
             collections: [
               {
                 fields: [
@@ -221,7 +259,7 @@ describe('config', () => {
     it('should not throw if collection fields are unique across nesting levels', () => {
       expect(() => {
         validateConfig(
-          merge(validConfig, {
+          merge({}, validConfig, {
             collections: [
               {
                 fields: [
@@ -257,7 +295,7 @@ describe('config', () => {
       it('should throw if nested relation displayFields and searchFields are not arrays', () => {
         expect(() => {
           validateConfig(
-            merge(validConfig, {
+            merge({}, validConfig, {
               collections: [
                 {
                   fields: [
@@ -288,7 +326,7 @@ describe('config', () => {
       it('should not throw if nested relation displayFields and searchFields are arrays', () => {
         expect(() => {
           validateConfig(
-            merge(validConfig, {
+            merge({}, validConfig, {
               collections: [
                 {
                   fields: [
@@ -358,5 +396,45 @@ describe('config', () => {
         );
       }).not.toThrow();
     });
+
+    it('should throw if collection field pattern is not an array', () => {
+      expect(() => {
+        validateConfig(merge({}, validConfig, { collections: [{ fields: [{ pattern: '' }] }] }));
+      }).toThrowError("'collections[0].fields[0].pattern' should be array");
+    });
+
+    it('should throw if collection field pattern is not an array of [string|regex, string]', () => {
+      expect(() => {
+        validateConfig(
+          merge({}, validConfig, { collections: [{ fields: [{ pattern: [1, ''] }] }] }),
+        );
+      }).toThrowError(
+        "'collections[0].fields[0].pattern[0]' should be string\n'collections[0].fields[0].pattern[0]' should be a regular expression",
+      );
+
+      expect(() => {
+        validateConfig(
+          merge({}, validConfig, { collections: [{ fields: [{ pattern: ['', 1] }] }] }),
+        );
+      }).toThrowError("'collections[0].fields[0].pattern[1]' should be string");
+    });
+
+    it('should allow collection field pattern to be an array of [string|regex, string]', () => {
+      expect(() => {
+        validateConfig(
+          merge({}, validConfig, {
+            collections: [{ fields: [{ pattern: ['pattern', 'error'] }] }],
+          }),
+        );
+      }).not.toThrow();
+
+      expect(() => {
+        validateConfig(
+          merge({}, validConfig, {
+            collections: [{ fields: [{ pattern: [/pattern/, 'error'] }] }],
+          }),
+        );
+      }).not.toThrow();
+    });
   });
 });
diff --git a/packages/netlify-cms-core/src/constants/configSchema.js b/packages/netlify-cms-core/src/constants/configSchema.js
index ee714d51..b1269830 100644
--- a/packages/netlify-cms-core/src/constants/configSchema.js
+++ b/packages/netlify-cms-core/src/constants/configSchema.js
@@ -1,5 +1,5 @@
 import AJV from 'ajv';
-import { select, uniqueItemProperties } from 'ajv-keywords/keywords';
+import { select, uniqueItemProperties, instanceof as instanceOf } from 'ajv-keywords/keywords';
 import ajvErrors from 'ajv-errors';
 import { formatExtensions, frontmatterFormats, extensionFormatters } from 'Formats/formats';
 import { getWidgets } from 'Lib/registry';
@@ -21,7 +21,11 @@ const fieldsConfig = () => ({
       widget: { type: 'string' },
       required: { type: 'boolean' },
       hint: { type: 'string' },
-      pattern: { type: 'array', minItems: 2, items: { type: 'string' } },
+      pattern: {
+        type: 'array',
+        minItems: 2,
+        items: [{ oneOf: [{ type: 'string' }, { instanceof: 'RegExp' }] }, { type: 'string' }],
+      },
       field: { $ref: 'field' },
       fields: { $ref: 'fields' },
       types: { $ref: 'fields' },
@@ -274,25 +278,40 @@ export function validateConfig(config) {
   const ajv = new AJV({ allErrors: true, jsonPointers: true, $data: true });
   uniqueItemProperties(ajv);
   select(ajv);
+  instanceOf(ajv);
   ajvErrors(ajv);
 
   const valid = ajv.validate(getConfigSchema(), config);
   if (!valid) {
     const errors = ajv.errors.map(e => {
-      // TODO: remove after https://github.com/ajv-validator/ajv-keywords/pull/123 is merged
-      if (e.keyword === 'uniqueItemProperties') {
-        const path = e.dataPath || '';
-        let newError = e;
-        if (path.endsWith('/fields')) {
-          newError = { ...e, message: 'fields names must be unique' };
-        } else if (path.endsWith('/files')) {
-          newError = { ...e, message: 'files names must be unique' };
-        } else if (path.endsWith('/collections')) {
-          newError = { ...e, message: 'collections names must be unique' };
+      switch (e.keyword) {
+        // TODO: remove after https://github.com/ajv-validator/ajv-keywords/pull/123 is merged
+        case 'uniqueItemProperties': {
+          const path = e.dataPath || '';
+          let newError = e;
+          if (path.endsWith('/fields')) {
+            newError = { ...e, message: 'fields names must be unique' };
+          } else if (path.endsWith('/files')) {
+            newError = { ...e, message: 'files names must be unique' };
+          } else if (path.endsWith('/collections')) {
+            newError = { ...e, message: 'collections names must be unique' };
+          }
+          return newError;
         }
-        return newError;
+        case 'instanceof': {
+          const path = e.dataPath || '';
+          let newError = e;
+          if (/fields\/\d+\/pattern\/\d+/.test(path)) {
+            newError = {
+              ...e,
+              message: 'should be a regular expression',
+            };
+          }
+          return newError;
+        }
+        default:
+          return e;
       }
-      return e;
     });
     console.error('Config Errors', errors);
     throw new ConfigError(errors);