diff --git a/src/cmd/go/internal/work/gc.go b/src/cmd/go/internal/work/gc.go
index 57024694cf6..daa88d31143 100644
--- a/src/cmd/go/internal/work/gc.go
+++ b/src/cmd/go/internal/work/gc.go
@@ -227,7 +227,7 @@ func (a *Action) trimpath() string {
 	// For "go build -trimpath", rewrite package source directory
 	// to a file system-independent path (just the import path).
 	if cfg.BuildTrimpath {
-		if m := a.Package.Module; m != nil {
+		if m := a.Package.Module; m != nil && m.Dir != "" && m.Version != "" {
 			rewrite += ";" + m.Dir + "=>" + m.Path + "@" + m.Version
 		} else {
 			rewrite += ";" + a.Package.Dir + "=>" + a.Package.ImportPath
diff --git a/src/cmd/go/testdata/script/mod_vendor_trimpath.txt b/src/cmd/go/testdata/script/mod_vendor_trimpath.txt
new file mode 100644
index 00000000000..241a3036751
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_vendor_trimpath.txt
@@ -0,0 +1,40 @@
+# Check that when -trimpath and -mod=vendor are used together,
+# paths in vendored packages are properly trimmed.
+# Verifies golang.org/issue/36566.
+
+[short] skip
+
+# Only the main module has a root directory in vendor mode.
+go mod vendor
+go list -f {{.Module.Dir}} example.com/main
+stdout $PWD
+go list -f {{.Module.Dir}} example.com/stack
+! stdout .
+
+# The program prints a file name from a vendored package.
+# Without -trimpath, the name should include the vendor directory.
+go run main.go
+stdout vendor
+
+# With -trimpath, everything before the package path should be trimmed.
+# Unlike with -mod=mod, we don't include versions as part of the module name.
+go run -trimpath main.go
+stdout example.com/stack/stack.go
+
+-- go.mod --
+module example.com/main
+
+require example.com/stack v1.0.0
+
+-- main.go --
+package main
+
+import (
+  "fmt"
+
+  "example.com/stack"
+)
+
+func main() {
+  fmt.Println(stack.TopFile())
+}