diff --git a/garden-service/src/config/common.ts b/garden-service/src/config/common.ts
index 5778c338f8..47ae66fbaf 100644
--- a/garden-service/src/config/common.ts
+++ b/garden-service/src/config/common.ts
@@ -200,7 +200,7 @@ export const joiIdentifierMap = (valueSchema: JoiObject) => joi
   .description("Key/value map. Keys must be valid identifiers.")
 
 export const joiVariables = () => joi
-  .object().pattern(/[\w\d]+/i, joiPrimitive())
+  .object().pattern(/[a-zA-Z][a-zA-Z0-9_\-]+/i, joiPrimitive())
   .default(() => ({}), "{}")
   .unknown(false)
   .description("Key/value map. Keys may contain letters and numbers, and values must be primitives.")
diff --git a/garden-service/src/config/module.ts b/garden-service/src/config/module.ts
index 8330918b4f..a459bf7599 100644
--- a/garden-service/src/config/module.ts
+++ b/garden-service/src/config/module.ts
@@ -23,6 +23,7 @@ import {
 import { TestConfig, TestSpec, testConfigSchema } from "./test"
 import { TaskConfig, TaskSpec, taskConfigSchema } from "./task"
 import { DEFAULT_API_VERSION } from "../constants"
+import { joiVariables } from "./common"
 
 export interface BuildCopySpec {
   source: string
@@ -173,7 +174,7 @@ export interface ModuleConfig
 
 export const moduleConfigSchema = baseModuleSpecSchema
   .keys({
-    outputs: joiIdentifierMap(joiPrimitive())
+    outputs: joiVariables()
       .description("The outputs defined by the module (referenceable in other module configs)."),
     path: joi.string()
       .description("The filesystem path of the module."),
diff --git a/garden-service/src/config/service.ts b/garden-service/src/config/service.ts
index 123ea3d0d9..003384399e 100644
--- a/garden-service/src/config/service.ts
+++ b/garden-service/src/config/service.ts
@@ -7,7 +7,7 @@
  */
 
 import deline = require("deline")
-import { joiIdentifier, joiIdentifierMap, joiPrimitive, joiArray, joiUserIdentifier, joi } from "./common"
+import { joiIdentifier, joiArray, joiUserIdentifier, joi, joiVariables } from "./common"
 
 export interface ServiceSpec { }
 
@@ -20,7 +20,7 @@ export interface CommonServiceSpec extends ServiceSpec {
   dependencies: string[]
 }
 
-export const serviceOutputsSchema = joiIdentifierMap(joiPrimitive())
+export const serviceOutputsSchema = joiVariables()
 
 export const dependenciesSchema = joiArray(joiIdentifier())
   .description(deline`