diff --git a/provisioner/windows-shell/provisioner.go b/provisioner/windows-shell/provisioner.go
index 6d37e2514..993c92ab2 100644
--- a/provisioner/windows-shell/provisioner.go
+++ b/provisioner/windows-shell/provisioner.go
@@ -40,7 +40,7 @@ type Config struct {
 
 	// This is used in the template generation to format environment variables
 	// inside the `ExecuteCommand` template.
-	EnvVarFormat string
+	EnvVarFormat string `mapstructure:"env_var_format"`
 
 	ctx interpolate.Context
 }