diff --git a/common-errors.go b/common-errors.go
index 0a9cc11..b28007f 100644
--- a/common-errors.go
+++ b/common-errors.go
@@ -25,15 +25,11 @@ func errTooMuchParams(funcName string, maxArgs, argCount int) (err error) {
 // --- General errors
 
 func errCantConvert(funcName string, value any, kind string) error {
-	if typer, ok := value.(Typer); ok {
-		return fmt.Errorf("%s(): can't convert %s to %s", funcName, typer.TypeName(), kind)
-	} else {
-		return fmt.Errorf("%s(): can't convert %T to %s", funcName, value, kind)
-	}
+	return fmt.Errorf("%s(): can't convert %s to %s", funcName, typeName(value), kind)
 }
 
 func errExpectedGot(funcName string, kind string, value any) error {
-	return fmt.Errorf("%s() expected %s, got %T (%v)", funcName, kind, value, value)
+	return fmt.Errorf("%s() expected %s, got %s (%v)", funcName, kind, typeName(value), value)
 }
 
 func errFuncDivisionByZero(funcName string) error {
@@ -46,18 +42,14 @@ func errDivisionByZero() error {
 
 // --- Parameter errors
 
-// func errOneParam(funcName string) error {
-// 	return fmt.Errorf("%s() requires exactly one param", funcName)
-// }
-
 func errMissingRequiredParameter(funcName, paramName string) error {
 	return fmt.Errorf("%s() missing required parameter %q", funcName, paramName)
 }
 
 func errInvalidParameterValue(funcName, paramName string, paramValue any) error {
-	return fmt.Errorf("%s() invalid value %T (%v) for parameter %q", funcName, paramValue, paramValue, paramName)
+	return fmt.Errorf("%s() invalid value %s (%v) for parameter %q", funcName, typeName(paramValue), paramValue, paramName)
 }
 
 func errWrongParamType(funcName, paramName, paramType string, paramValue any) error {
-	return fmt.Errorf("%s() the %q parameter must be a %s, got a %T (%v)", funcName, paramName, paramType, paramValue, paramValue)
+	return fmt.Errorf("%s() the %q parameter must be a %s, got a %s (%v)", funcName, paramName, paramType, typeName(paramValue), paramValue)
 }
diff --git a/formatter.go b/formatter.go
index eb6e654..be0d911 100644
--- a/formatter.go
+++ b/formatter.go
@@ -51,8 +51,10 @@ type Typer interface {
 	TypeName() string
 }
 
-func getTypeName(v any) (name string) {
-	if typer, ok := v.(Typer); ok {
+func typeName(v any) (name string) {
+	if v == nil {
+		name = "nil"
+	} else if typer, ok := v.(Typer); ok {
 		name = typer.TypeName()
 	} else if IsInteger(v) {
 		name = "integer"
diff --git a/term.go b/term.go
index 325eaa4..fae9b58 100644
--- a/term.go
+++ b/term.go
@@ -156,15 +156,15 @@ func (self *term) toInt(computedValue any, valueDescription string) (i int, err
 	if index64, ok := computedValue.(int64); ok {
 		i = int(index64)
 	} else {
-		err = self.Errorf("%s, got %T (%v)", valueDescription, computedValue, computedValue)
+		err = self.Errorf("%s, got %s (%v)", valueDescription, typeName(computedValue), computedValue)
 	}
 	return
 }
 
 func (self *term) errIncompatibleTypes(leftValue, rightValue any) error {
-	leftType := getTypeName(leftValue)
+	leftType := typeName(leftValue)
 	leftText := getFormatted(leftValue, Truncate)
-	rightType := getTypeName(rightValue)
+	rightType := typeName(rightValue)
 	rightText := getFormatted(rightValue, Truncate)
 	return self.tk.Errorf(
 		"left operand '%s' [%s] and right operand '%s' [%s] are not compatible with operator %q",
@@ -175,8 +175,8 @@ func (self *term) errIncompatibleTypes(leftValue, rightValue any) error {
 
 func (self *term) errIncompatibleType(value any) error {
 	return self.tk.Errorf(
-		"prefix/postfix operator %q do not support operand '%v' [%T]",
-		self.source(), value, value)
+		"prefix/postfix operator %q do not support operand '%v' [%s]",
+		self.source(), value, typeName(value))
 }
 
 func (self *term) Errorf(template string, args ...any) (err error) {