diff --git a/src/google-types.ts b/src/google-types.ts
index 25cc9e7..db8b6e8 100644
--- a/src/google-types.ts
+++ b/src/google-types.ts
@@ -134,6 +134,16 @@ export class GoogleTypes {
         'HALF',
         'YEAR',
       ],
+      'x-enum-mapping': {
+        CALENDAR_PERIOD_UNSPECIFIED: 0,
+        DAY: 1,
+        WEEK: 2,
+        FORTNIGHT: 3,
+        MONTH: 4,
+        QUARTER: 5,
+        HALF: 6,
+        YEAR: 7,
+      },
       description:
         'A `CalendarPeriod` represents the abstract concept of a time period that has a canonical start. Grammatically, "the start of the current  `CalendarPeriod`." All calendar times begin at midnight UTC.',
     },
@@ -498,6 +508,21 @@ export class GoogleTypes {
         'NOVEMBER',
         'DECEMBER',
       ],
+      'x-enum-mapping': {
+        MONTH_UNSPECIFIED: 0,
+        JANUARY: 1,
+        FEBRUARY: 2,
+        MARCH: 3,
+        APRIL: 4,
+        MAY: 5,
+        JUNE: 6,
+        JULY: 7,
+        AUGUST: 8,
+        SEPTEMBER: 9,
+        OCTOBER: 10,
+        NOVEMBER: 11,
+        DECEMBER: 12,
+      },
       description: 'Represents a month in the Gregorian calendar.',
     },
     'google.type.PostalAddress': {
diff --git a/src/protoj2jsonSchema.ts b/src/protoj2jsonSchema.ts
index 6ea7131..81b8da3 100644
--- a/src/protoj2jsonSchema.ts
+++ b/src/protoj2jsonSchema.ts
@@ -286,10 +286,16 @@ class Proto2JsonSchema {
   private compileEnum(
     enumType: InternalEnum
   ): SpecTypesV2.AsyncAPISchemaDefinition {
+    const enumMapping: {[key: string]: number} = {};
+    for (const enumKey of Object.keys(enumType.values)) {
+      enumMapping[enumKey] = enumType.values[enumKey].value;
+    }
+    
     return {
       title: enumType.name,
       type: 'string',
       enum: Object.keys(enumType.values),
+      'x-enum-mapping': enumMapping
     };
   }
 
diff --git a/test/documents/realworld.train_run.proto.result.json b/test/documents/realworld.train_run.proto.result.json
index fb18a26..a73f01a 100644
--- a/test/documents/realworld.train_run.proto.result.json
+++ b/test/documents/realworld.train_run.proto.result.json
@@ -216,6 +216,13 @@
                           "AFDZ_MANUELL_ERGAENZT",
                           "AFDZ_OK"
                         ],
+                        "x-enum-mapping": {
+                          "AFDZ_UNSPECIFIED": 0,
+                          "AFDZ_KEINE_TRAKTION": 1,
+                          "AFDZ_ANHAENGELAST_FEHLT": 2,
+                          "AFDZ_MANUELL_ERGAENZT": 3,
+                          "AFDZ_OK": 4
+                        },
 
                       },
                       "anzahl_loks": {
@@ -621,6 +628,13 @@
                             "FS_NORMAL",
                             "FS_FAHRZEIT_VERTEILEN"
                           ],
+                          "x-enum-mapping": {
+                            "FS_UNSPECIFIED": 0,
+                            "FS_SCHNELL": 1,
+                            "FS_HALTEN": 2,
+                            "FS_NORMAL": 3,
+                            "FS_FAHRZEIT_VERTEILEN": 4
+                          },
 
                         }
                       },
@@ -680,6 +694,13 @@
                             "TST_D",
                             "TST_N"
                           ],
+                          "x-enum-mapping": {
+                            "TST_UNSPECIFIED": 0,
+                            "TST_R": 1,
+                            "TST_A": 2,
+                            "TST_D": 3,
+                            "TST_N": 4
+                          },
 
                         }
                       },
@@ -714,6 +735,13 @@
                         "AOSS_OBSERVE_EARLIEST_TIMES",
                         "AOSS_ONLY_WHEN_ROUTE_IS_SET"
                       ],
+                      "x-enum-mapping": {
+                        "AOSS_UNSPECIFIED": 0,
+                        "AOSS_ALLOWED": 1,
+                        "AOSS_PROHIBITED": 2,
+                        "AOSS_OBSERVE_EARLIEST_TIMES": 4,
+                        "AOSS_ONLY_WHEN_ROUTE_IS_SET": 5
+                      },
 
                     }
                   },
@@ -791,6 +819,13 @@
                       "AFDZ_MANUELL_ERGAENZT",
                       "AFDZ_OK"
                     ],
+                    "x-enum-mapping": {
+                      "AFDZ_UNSPECIFIED": 0,
+                      "AFDZ_KEINE_TRAKTION": 1,
+                      "AFDZ_ANHAENGELAST_FEHLT": 2,
+                      "AFDZ_MANUELL_ERGAENZT": 3,
+                      "AFDZ_OK": 4
+                    },
 
                   },
                   "anzahl_loks": {
@@ -1043,6 +1078,13 @@
                         "AFDZ_MANUELL_ERGAENZT",
                         "AFDZ_OK"
                       ],
+                      "x-enum-mapping": {
+                        "AFDZ_UNSPECIFIED": 0,
+                        "AFDZ_KEINE_TRAKTION": 1,
+                        "AFDZ_ANHAENGELAST_FEHLT": 2,
+                        "AFDZ_MANUELL_ERGAENZT": 3,
+                        "AFDZ_OK": 4
+                      },
 
                     },
                     "anzahl_loks": {
@@ -1448,6 +1490,13 @@
                           "FS_NORMAL",
                           "FS_FAHRZEIT_VERTEILEN"
                         ],
+                        "x-enum-mapping": {
+                          "FS_UNSPECIFIED": 0,
+                          "FS_SCHNELL": 1,
+                          "FS_HALTEN": 2,
+                          "FS_NORMAL": 3,
+                          "FS_FAHRZEIT_VERTEILEN": 4
+                        },
 
                       }
                     },
@@ -1507,6 +1556,13 @@
                           "TST_D",
                           "TST_N"
                         ],
+                        "x-enum-mapping": {
+                          "TST_UNSPECIFIED": 0,
+                          "TST_R": 1,
+                          "TST_A": 2,
+                          "TST_D": 3,
+                          "TST_N": 4
+                        },
 
                       }
                     },
@@ -1541,6 +1597,13 @@
                       "AOSS_OBSERVE_EARLIEST_TIMES",
                       "AOSS_ONLY_WHEN_ROUTE_IS_SET"
                     ],
+                    "x-enum-mapping": {
+                      "AOSS_UNSPECIFIED": 0,
+                      "AOSS_ALLOWED": 1,
+                      "AOSS_PROHIBITED": 2,
+                      "AOSS_OBSERVE_EARLIEST_TIMES": 4,
+                      "AOSS_ONLY_WHEN_ROUTE_IS_SET": 5
+                    },
 
                   }
                 },
@@ -1618,6 +1681,13 @@
                     "AFDZ_MANUELL_ERGAENZT",
                     "AFDZ_OK"
                   ],
+                  "x-enum-mapping": {
+                    "AFDZ_UNSPECIFIED": 0,
+                    "AFDZ_KEINE_TRAKTION": 1,
+                    "AFDZ_ANHAENGELAST_FEHLT": 2,
+                    "AFDZ_MANUELL_ERGAENZT": 3,
+                    "AFDZ_OK": 4
+                  },
 
                 },
                 "anzahl_loks": {