diff --git a/garden-service/package-lock.json b/garden-service/package-lock.json
index 1250fb90a9..b18a1497a9 100644
--- a/garden-service/package-lock.json
+++ b/garden-service/package-lock.json
@@ -5603,8 +5603,7 @@
             "ansi-regex": {
               "version": "2.1.1",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             },
             "aproba": {
               "version": "1.2.0",
@@ -5625,14 +5624,12 @@
             "balanced-match": {
               "version": "1.0.0",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             },
             "brace-expansion": {
               "version": "1.1.11",
               "bundled": true,
               "dev": true,
-              "optional": true,
               "requires": {
                 "balanced-match": "^1.0.0",
                 "concat-map": "0.0.1"
@@ -5647,20 +5644,17 @@
             "code-point-at": {
               "version": "1.1.0",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             },
             "concat-map": {
               "version": "0.0.1",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             },
             "console-control-strings": {
               "version": "1.1.0",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             },
             "core-util-is": {
               "version": "1.0.2",
@@ -5777,8 +5771,7 @@
             "inherits": {
               "version": "2.0.3",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             },
             "ini": {
               "version": "1.3.5",
@@ -5790,7 +5783,6 @@
               "version": "1.0.0",
               "bundled": true,
               "dev": true,
-              "optional": true,
               "requires": {
                 "number-is-nan": "^1.0.0"
               }
@@ -5805,7 +5797,6 @@
               "version": "3.0.4",
               "bundled": true,
               "dev": true,
-              "optional": true,
               "requires": {
                 "brace-expansion": "^1.1.7"
               }
@@ -5813,14 +5804,12 @@
             "minimist": {
               "version": "0.0.8",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             },
             "minipass": {
               "version": "2.3.5",
               "bundled": true,
               "dev": true,
-              "optional": true,
               "requires": {
                 "safe-buffer": "^5.1.2",
                 "yallist": "^3.0.0"
@@ -5839,7 +5828,6 @@
               "version": "0.5.1",
               "bundled": true,
               "dev": true,
-              "optional": true,
               "requires": {
                 "minimist": "0.0.8"
               }
@@ -5920,8 +5908,7 @@
             "number-is-nan": {
               "version": "1.0.1",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             },
             "object-assign": {
               "version": "4.1.1",
@@ -5933,7 +5920,6 @@
               "version": "1.4.0",
               "bundled": true,
               "dev": true,
-              "optional": true,
               "requires": {
                 "wrappy": "1"
               }
@@ -6019,8 +6005,7 @@
             "safe-buffer": {
               "version": "5.1.2",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             },
             "safer-buffer": {
               "version": "2.1.2",
@@ -6056,7 +6041,6 @@
               "version": "1.0.2",
               "bundled": true,
               "dev": true,
-              "optional": true,
               "requires": {
                 "code-point-at": "^1.0.0",
                 "is-fullwidth-code-point": "^1.0.0",
@@ -6076,7 +6060,6 @@
               "version": "3.0.1",
               "bundled": true,
               "dev": true,
-              "optional": true,
               "requires": {
                 "ansi-regex": "^2.0.0"
               }
@@ -6120,14 +6103,12 @@
             "wrappy": {
               "version": "1.0.2",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             },
             "yallist": {
               "version": "3.0.3",
               "bundled": true,
-              "dev": true,
-              "optional": true
+              "dev": true
             }
           }
         },
@@ -11383,8 +11364,7 @@
     "slash": {
       "version": "3.0.0",
       "resolved": "https://registry.npmjs.org/slash/-/slash-3.0.0.tgz",
-      "integrity": "sha512-g9Q1haeby36OSStwb4ntCGGGaKsaVSjQ68fBxoQcutl5fS1vuY18H3wSt3jFyFtrkx+Kz0V1G85A4MyAdDMi2Q==",
-      "dev": true
+      "integrity": "sha512-g9Q1haeby36OSStwb4ntCGGGaKsaVSjQ68fBxoQcutl5fS1vuY18H3wSt3jFyFtrkx+Kz0V1G85A4MyAdDMi2Q=="
     },
     "slice-ansi": {
       "version": "3.0.0",
diff --git a/garden-service/package.json b/garden-service/package.json
index d8d1377929..38371fa07c 100644
--- a/garden-service/package.json
+++ b/garden-service/package.json
@@ -107,6 +107,7 @@
     "recursive-readdir": "^2.2.2",
     "request": "^2.88.2",
     "request-promise": "^4.2.5",
+    "slash": "^3.0.0",
     "source-map-support": "^0.5.16",
     "split": "^1.0.1",
     "split2": "^3.1.1",
diff --git a/garden-service/src/plugins/conftest/conftest-kubernetes.ts b/garden-service/src/plugins/conftest/conftest-kubernetes.ts
index a66b593712..2057d8e094 100644
--- a/garden-service/src/plugins/conftest/conftest-kubernetes.ts
+++ b/garden-service/src/plugins/conftest/conftest-kubernetes.ts
@@ -7,6 +7,7 @@
  */
 
 import Bluebird from "bluebird"
+import slash from "slash"
 import { createGardenPlugin } from "../../types/plugin/plugin"
 import { ConftestProvider } from "./conftest"
 import { relative, resolve } from "path"
@@ -65,7 +66,8 @@ export const gardenPlugin = createGardenPlugin({
             ? [".rendered.yaml"]
             : module.include || ["*.yaml", "**/*.yaml", "*.yml", "**/*.yml"]
 
-          const policyPath = relative(module.path, resolve(ctx.projectRoot, provider.config.policyPath))
+          // Make sure the policy path is valid POSIX on Windows
+          const policyPath = slash(relative(module.path, resolve(ctx.projectRoot, provider.config.policyPath)))
 
           return {
             kind: "Module",
diff --git a/garden-service/src/plugins/conftest/conftest.ts b/garden-service/src/plugins/conftest/conftest.ts
index 4d89f12346..8186e5e58d 100644
--- a/garden-service/src/plugins/conftest/conftest.ts
+++ b/garden-service/src/plugins/conftest/conftest.ts
@@ -19,6 +19,7 @@ import { baseBuildSpecSchema } from "../../config/module"
 import { matchGlobs, listDirectory } from "../../util/fs"
 import { PluginError } from "../../exceptions"
 import { getModuleTypeUrl, getGitHubUrl, getProviderUrl } from "../../docs/common"
+import slash from "slash"
 
 export interface ConftestProviderConfig extends ProviderConfig {
   policyPath: string
@@ -135,7 +136,8 @@ export const gardenPlugin = createGardenPlugin({
           const provider = ctx.provider as ConftestProvider
 
           const defaultPolicyPath = relative(module.path, resolve(ctx.projectRoot, provider.config.policyPath))
-          const policyPath = resolve(module.path, module.spec.policyPath || defaultPolicyPath)
+          // Make sure the policy path is valid POSIX on Windows
+          const policyPath = slash(resolve(module.path, module.spec.policyPath || defaultPolicyPath))
           const namespace = module.spec.namespace || provider.config.namespace
 
           const buildPath = module.spec.sourceModule