--- a/crates/jsonnet-evaluator/src/error.rs
+++ b/crates/jsonnet-evaluator/src/error.rs
@@ -16,6 +16,10 @@
 
 	FieldMustBeStringGot(ValType),
 
+	AttemptedIndexAnArrayWithString(String),
+	ValueIndexMustBeTypeGot(ValType, ValType, ValType),
+	CantIndexInto(ValType),
+
 	RuntimeError(String),
 	StackOverflow,
 	FractionalIndex,
--- a/crates/jsonnet-evaluator/src/evaluate.rs
+++ b/crates/jsonnet-evaluator/src/evaluate.rs
@@ -421,6 +421,12 @@
 						create_error(crate::Error::NoSuchField(s))?
 					}
 				}
+				(Val::Obj(_), n) => create_error(crate::Error::ValueIndexMustBeTypeGot(
+					ValType::Obj,
+					ValType::Str,
+					n.value_type()?,
+				))?,
+
 				(Val::Arr(v), Val::Num(n)) => {
 					if n.fract() > f64::EPSILON {
 						create_error(crate::Error::FractionalIndex)?
@@ -430,10 +436,25 @@
 						.clone()
 						.unwrap_if_lazy()?
 				}
+				(Val::Arr(_), Val::Str(n)) => {
+					create_error(crate::Error::AttemptedIndexAnArrayWithString(n))?
+				}
+				(Val::Arr(_), n) => create_error(crate::Error::ValueIndexMustBeTypeGot(
+					ValType::Arr,
+					ValType::Num,
+					n.value_type()?,
+				))?,
+
 				(Val::Str(s), Val::Num(n)) => {
 					Val::Str(s.chars().skip(n as usize).take(1).collect())
 				}
-				(v, i) => todo!("not implemented: {:?}[{:?}]", v, i.unwrap_if_lazy()),
+				(Val::Str(_), n) => create_error(crate::Error::ValueIndexMustBeTypeGot(
+					ValType::Str,
+					ValType::Num,
+					n.value_type()?,
+				))?,
+
+				(v, _) => create_error(crate::Error::CantIndexInto(v.value_type()?))?,
 			}
 		}
 		LocalExpr(bindings, returned) => {