diff --git a/src/ast.rs b/src/ast.rs
index 1a3c82a..b212278 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -502,6 +502,8 @@ impl Formula
 
 	pub fn exists(parameters: std::rc::Rc<VariableDeclarations>, argument: Box<Formula>) -> Self
 	{
+		assert!(!parameters.is_empty());
+
 		Self::Exists(Exists::new(parameters, argument))
 	}
 
@@ -517,6 +519,8 @@ impl Formula
 
 	pub fn for_all(parameters: std::rc::Rc<VariableDeclarations>, argument: Box<Formula>) -> Self
 	{
+		assert!(!parameters.is_empty());
+
 		Self::ForAll(ForAll::new(parameters, argument))
 	}
 
diff --git a/src/format.rs b/src/format.rs
index 2ebfba3..925f976 100644
--- a/src/format.rs
+++ b/src/format.rs
@@ -205,6 +205,8 @@ impl<'formula> std::fmt::Debug for FormulaDisplay<'formula>
 		{
 			crate::Formula::Exists(exists) =>
 			{
+				assert!(!exists.parameters.is_empty());
+
 				write!(format, "exists")?;
 
 				let mut separator = " ";
@@ -220,6 +222,8 @@ impl<'formula> std::fmt::Debug for FormulaDisplay<'formula>
 			},
 			crate::Formula::ForAll(for_all) =>
 			{
+				assert!(!for_all.parameters.is_empty());
+
 				write!(format, "forall")?;
 
 				let mut separator = " ";