diff --git a/ihatemoney/api/common.py b/ihatemoney/api/common.py
index cd247cdf..ede76e46 100644
--- a/ihatemoney/api/common.py
+++ b/ihatemoney/api/common.py
@@ -69,7 +69,7 @@ class ProjectHandler(Resource):
         return "DELETED"
 
     def put(self, project):
-        form = EditProjectForm(meta={"csrf": False})
+        form = EditProjectForm(id=project.id, meta={"csrf": False})
         if form.validate() and current_app.config.get("ALLOW_PUBLIC_PROJECT_CREATION"):
             form.update(project)
             db.session.commit()
diff --git a/ihatemoney/forms.py b/ihatemoney/forms.py
index fcb9f9a4..2085ffe1 100644
--- a/ihatemoney/forms.py
+++ b/ihatemoney/forms.py
@@ -1,5 +1,6 @@
 from datetime import datetime
 from re import match
+from types import SimpleNamespace
 
 import email_validator
 from flask import request
@@ -110,6 +111,10 @@ class EditProjectForm(FlaskForm):
     default_currency = SelectField(_("Default Currency"), validators=[DataRequired()])
 
     def __init__(self, *args, **kwargs):
+        if not hasattr(self, "id"):
+            # We must access the project to validate the default currency.
+            # Mimics a StringField. Defaut to empty string to ensure that query run smoothly.
+            self.id = SimpleNamespace(data=kwargs.pop("id", ""))
         super().__init__(*args, **kwargs)
         self.default_currency.choices = [
             (currency_name, render_localized_currency(currency_name, detailed=True))
@@ -142,6 +147,23 @@ class EditProjectForm(FlaskForm):
         )
         return project
 
+    def validate_default_currency(form, field):
+        project = Project.query.get(form.id.data)
+        if (
+            project is not None
+            and field.data == CurrencyConverter.no_currency
+            and project.has_multiple_currencies()
+        ):
+            raise ValidationError(
+                _(
+                    (
+                        "This project already uses different currencies"
+                        "and can't be set to 'No Currency'"
+                    )
+                )
+            )
+        pass
+
     def update(self, project):
         """Update the project with the information from the form"""
         project.name = self.name.data
diff --git a/ihatemoney/web.py b/ihatemoney/web.py
index c0afab91..41940b30 100644
--- a/ihatemoney/web.py
+++ b/ihatemoney/web.py
@@ -399,7 +399,7 @@ def reset_password():
 
 @main.route("/<project_id>/edit", methods=["GET", "POST"])
 def edit_project():
-    edit_form = EditProjectForm()
+    edit_form = EditProjectForm(id=g.project.id)
     import_form = UploadForm()
     # Import form
     if import_form.validate_on_submit():