diff --git a/builtins.go b/builtins.go
index bc15ff8..421d5d3 100644
--- a/builtins.go
+++ b/builtins.go
@@ -345,6 +345,19 @@ func builtinFlatMap(i *interpreter, funcv, arrv value) (value, error) {
 	}
 }
 
+// builtinFlatMapArray is like builtinFlatMap, but only accepts array as the
+// arrv value. Desugared comprehensions contain a call to this function, rather
+// than builtinFlatMap, so that a better error message is printed when the
+// comprehension would iterate over a non-array.
+func builtinFlatMapArray(i *interpreter, funcv, arrv value) (value, error) {
+	switch arrv := arrv.(type) {
+	case *valueArray:
+		return builtinFlatMap(i, funcv, arrv)
+	default:
+		return nil, i.typeErrorSpecific(arrv, &valueArray{})
+	}
+}
+
 func joinArrays(i *interpreter, sep *valueArray, arr *valueArray) (value, error) {
 	result := make([]*cachedThunk, 0, arr.length())
 	first := true
@@ -2880,4 +2893,5 @@ var funcBuiltins = buildBuiltinMap([]builtin{
 
 	// internal
 	&unaryBuiltin{name: "$objectFlatMerge", function: builtinUglyObjectFlatMerge, params: ast.Identifiers{"x"}},
+	&binaryBuiltin{name: "$flatMapArray", function: builtinFlatMapArray, params: ast.Identifiers{"func", "arr"}},
 })
diff --git a/internal/program/desugarer.go b/internal/program/desugarer.go
index d36acbe..763a729 100644
--- a/internal/program/desugarer.go
+++ b/internal/program/desugarer.go
@@ -184,7 +184,7 @@ func desugarForSpec(inside ast.Node, loc ast.LocationRange, forSpec *ast.ForSpec
 	if err != nil {
 		return nil, err
 	}
-	current := buildStdCall("flatMap", loc, function, forSpec.Expr)
+	current := buildStdCall("$flatMapArray", loc, function, forSpec.Expr)
 	if forSpec.Outer == nil {
 		return current, nil
 	}
diff --git a/linter/internal/types/stdlib.go b/linter/internal/types/stdlib.go
index 27c54a5..b1afb2d 100644
--- a/linter/internal/types/stdlib.go
+++ b/linter/internal/types/stdlib.go
@@ -199,6 +199,7 @@ func prepareStdlib(g *typeGraph) {
 		"mod":              g.newSimpleFuncType(stringOrNumber, "a", "b"),
 		"native":           g.newSimpleFuncType(anyFunctionType, "x"),
 		"$objectFlatMerge": g.newSimpleFuncType(anyObjectType, "x"),
+		"$flatMapArray":    g.newSimpleFuncType(anyArrayType, "func", "arr"),
 
 		// Boolean
 
diff --git a/testdata/array_comp_try_iterate_over_empty_string.golden b/testdata/array_comp_try_iterate_over_empty_string.golden
new file mode 100644
index 0000000..9112098
--- /dev/null
+++ b/testdata/array_comp_try_iterate_over_empty_string.golden
@@ -0,0 +1,10 @@
+RUNTIME ERROR: Unexpected type string, expected array
+-------------------------------------------------
+	testdata/array_comp_try_iterate_over_empty_string:1:1-16	
+
+[a for a in '']
+
+-------------------------------------------------
+	During evaluation	
+
+
diff --git a/testdata/array_comp_try_iterate_over_empty_string.jsonnet b/testdata/array_comp_try_iterate_over_empty_string.jsonnet
new file mode 100644
index 0000000..d081b80
--- /dev/null
+++ b/testdata/array_comp_try_iterate_over_empty_string.jsonnet
@@ -0,0 +1 @@
+[a for a in '']
diff --git a/testdata/array_comp_try_iterate_over_empty_string.linter.golden b/testdata/array_comp_try_iterate_over_empty_string.linter.golden
new file mode 100644
index 0000000..e69de29
diff --git a/testdata/array_comp_try_iterate_over_obj.golden b/testdata/array_comp_try_iterate_over_obj.golden
index 123943f..4a72d1d 100644
--- a/testdata/array_comp_try_iterate_over_obj.golden
+++ b/testdata/array_comp_try_iterate_over_obj.golden
@@ -1,4 +1,4 @@
-RUNTIME ERROR: std.flatMap second param must be array / string, got object
+RUNTIME ERROR: Unexpected type object, expected array
 -------------------------------------------------
 	testdata/array_comp_try_iterate_over_obj:1:1-16	
 
diff --git a/testdata/array_comp_try_iterate_over_string.golden b/testdata/array_comp_try_iterate_over_string.golden
new file mode 100644
index 0000000..fc9a815
--- /dev/null
+++ b/testdata/array_comp_try_iterate_over_string.golden
@@ -0,0 +1,10 @@
+RUNTIME ERROR: Unexpected type string, expected array
+-------------------------------------------------
+	testdata/array_comp_try_iterate_over_string:1:1-17	
+
+[a for a in 'b']
+
+-------------------------------------------------
+	During evaluation	
+
+
diff --git a/testdata/array_comp_try_iterate_over_string.jsonnet b/testdata/array_comp_try_iterate_over_string.jsonnet
new file mode 100644
index 0000000..05cd1e8
--- /dev/null
+++ b/testdata/array_comp_try_iterate_over_string.jsonnet
@@ -0,0 +1 @@
+[a for a in 'b']
diff --git a/testdata/array_comp_try_iterate_over_string.linter.golden b/testdata/array_comp_try_iterate_over_string.linter.golden
new file mode 100644
index 0000000..e69de29
diff --git a/testdata/object_comp_try_iterate_over_obj.golden b/testdata/object_comp_try_iterate_over_obj.golden
new file mode 100644
index 0000000..75df53e
--- /dev/null
+++ b/testdata/object_comp_try_iterate_over_obj.golden
@@ -0,0 +1,15 @@
+RUNTIME ERROR: Unexpected type object, expected array
+-------------------------------------------------
+	testdata/object_comp_try_iterate_over_obj:1:1-23	
+
+{ [a]: 0 for a in {} }
+
+-------------------------------------------------
+	testdata/object_comp_try_iterate_over_obj:1:1-23	
+
+{ [a]: 0 for a in {} }
+
+-------------------------------------------------
+	During evaluation	
+
+
diff --git a/testdata/object_comp_try_iterate_over_obj.jsonnet b/testdata/object_comp_try_iterate_over_obj.jsonnet
new file mode 100644
index 0000000..18b4289
--- /dev/null
+++ b/testdata/object_comp_try_iterate_over_obj.jsonnet
@@ -0,0 +1 @@
+{ [a]: 0 for a in {} }
diff --git a/testdata/object_comp_try_iterate_over_obj.linter.golden b/testdata/object_comp_try_iterate_over_obj.linter.golden
new file mode 100644
index 0000000..e69de29
diff --git a/testdata/object_comp_try_iterate_over_string.golden b/testdata/object_comp_try_iterate_over_string.golden
new file mode 100644
index 0000000..1841378
--- /dev/null
+++ b/testdata/object_comp_try_iterate_over_string.golden
@@ -0,0 +1,15 @@
+RUNTIME ERROR: Unexpected type string, expected array
+-------------------------------------------------
+	testdata/object_comp_try_iterate_over_string:1:1-24	
+
+{ [a]: 0 for a in 'b' }
+
+-------------------------------------------------
+	testdata/object_comp_try_iterate_over_string:1:1-24	
+
+{ [a]: 0 for a in 'b' }
+
+-------------------------------------------------
+	During evaluation	
+
+
diff --git a/testdata/object_comp_try_iterate_over_string.jsonnet b/testdata/object_comp_try_iterate_over_string.jsonnet
new file mode 100644
index 0000000..52a0610
--- /dev/null
+++ b/testdata/object_comp_try_iterate_over_string.jsonnet
@@ -0,0 +1 @@
+{ [a]: 0 for a in 'b' }
diff --git a/testdata/object_comp_try_iterate_over_string.linter.golden b/testdata/object_comp_try_iterate_over_string.linter.golden
new file mode 100644
index 0000000..e69de29