Fix Terraform Error - Invalid Default Value for Variable

The Error

When working with Terraform, you may encounter this error:

Error: Invalid default value for variable

This error can block your entire workflow. Let’s understand why it happens and how to fix it.

What Causes This Error

The default value doesn’t match the declared variable type constraint.

How to Fix It

Solution 1

Match the default to the type: type = list(string) needs default = [] not default = ""

Solution 2

For complex types, ensure nested structure matches: type = object({ name = string, port = number })

Solution 3

Remove the type constraint if the variable accepts mixed types.

Solution 4

Use terraform console to test type conversions.

Prevention Tips

• Always run terraform validate before terraform plan
• Use terraform fmt to keep configuration clean and readable
• Pin provider versions to avoid unexpected schema changes
• Review plan output carefully before applying

Learn More

• Terraform for Beginners Course — hands-on labs covering this topic
• Terraform By Example Book — real-world patterns and solutions
• Terraform Cheat Sheet — quick command reference

Related Articles

• All Troubleshooting Articles
• Terraform Glossary

Conclusion

This error is common but straightforward to fix. The key is understanding the root cause and applying the correct solution for your specific situation. Following the prevention tips above will help you avoid this error in future projects.