diff --git a/test/cases/testdata/aggregates/test-aggregates-0028.yaml b/test/cases/testdata/aggregates/test-aggregates-0028.yaml
new file mode 100644
index 0000000000..a80cd898ad
--- /dev/null
+++ b/test/cases/testdata/aggregates/test-aggregates-0028.yaml
@@ -0,0 +1,29 @@
+cases:
+- modules:
+  - |
+    package generated
+
+    p = x {
+      count(input.foo, x)
+    }
+  note: aggregates/count error null
+  query: data.generated.p = x
+  input:
+    foo: null
+  strict_error: true
+  want_error_code: eval_type_error
+  want_error: 'operand 1 must be one of {array, object, set, string} but got null'
+- modules:
+  - |
+    package generated
+
+    p = x {
+      count(input.foo, x)
+    }
+  note: aggregates/count error number
+  query: data.generated.p = x
+  input:
+    foo: 5
+  strict_error: true
+  want_error_code: eval_type_error
+  want_error: 'operand 1 must be one of {array, object, set, string} but got number'
diff --git a/test/cases/testdata/objectfilter/test-objectfilter-0314.yaml b/test/cases/testdata/objectfilter/test-objectfilter-0314.yaml
index 89efc74626..af808d8ebf 100644
--- a/test/cases/testdata/objectfilter/test-objectfilter-0314.yaml
+++ b/test/cases/testdata/objectfilter/test-objectfilter-0314.yaml
@@ -12,7 +12,6 @@ cases:
     }
   note: objectfilter/error invalid key param type string input
   query: data.generated.p = x
-  want_error: 'object.filter: operand 2 must be one of {object, string, array} but
-    got string'
+  want_error: 'object.filter: operand 2 must be one of {object, set, array} but got string'
   want_error_code: eval_type_error
   strict_error: true
diff --git a/test/cases/testdata/objectfilter/test-objectfilter-0315.yaml b/test/cases/testdata/objectfilter/test-objectfilter-0315.yaml
index 7e5ee7297f..b43d273919 100644
--- a/test/cases/testdata/objectfilter/test-objectfilter-0315.yaml
+++ b/test/cases/testdata/objectfilter/test-objectfilter-0315.yaml
@@ -12,7 +12,6 @@ cases:
     }
   note: objectfilter/error invalid key param type boolean input
   query: data.generated.p = x
-  want_error: 'object.filter: operand 2 must be one of {object, string, array} but
-    got boolean'
+  want_error: 'object.filter: operand 2 must be one of {object, set, array} but got boolean'
   want_error_code: eval_type_error
   strict_error: true
diff --git a/test/cases/testdata/objectfilter/test-objectfilter-0316.yaml b/test/cases/testdata/objectfilter/test-objectfilter-0316.yaml
index 43305dca96..b2b54243d7 100644
--- a/test/cases/testdata/objectfilter/test-objectfilter-0316.yaml
+++ b/test/cases/testdata/objectfilter/test-objectfilter-0316.yaml
@@ -12,7 +12,6 @@ cases:
     }
   note: objectfilter/error invalid key param type number input
   query: data.generated.p = x
-  want_error: 'object.filter: operand 2 must be one of {object, string, array} but
-    got number'
+  want_error: 'object.filter: operand 2 must be one of {object, set, array} but got number'
   want_error_code: eval_type_error
   strict_error: true
diff --git a/test/cases/testdata/objectfilter/test-objectfilter-0317.yaml b/test/cases/testdata/objectfilter/test-objectfilter-0317.yaml
index 4a4eb6e95c..8717b735a0 100644
--- a/test/cases/testdata/objectfilter/test-objectfilter-0317.yaml
+++ b/test/cases/testdata/objectfilter/test-objectfilter-0317.yaml
@@ -12,7 +12,6 @@ cases:
     }
   note: objectfilter/error invalid key param type nil input
   query: data.generated.p = x
-  want_error: 'object.filter: operand 2 must be one of {object, string, array} but
-    got null'
+  want_error: 'object.filter: operand 2 must be one of {object, set, array} but got null'
   want_error_code: eval_type_error
   strict_error: true
diff --git a/test/cases/testdata/objectremove/test-objectremove-0294.yaml b/test/cases/testdata/objectremove/test-objectremove-0294.yaml
index 918783e93a..946baac88b 100644
--- a/test/cases/testdata/objectremove/test-objectremove-0294.yaml
+++ b/test/cases/testdata/objectremove/test-objectremove-0294.yaml
@@ -12,7 +12,6 @@ cases:
     }
   note: objectremove/error invalid key param type string input
   query: data.generated.p = x
-  want_error: 'object.remove: operand 2 must be one of {object, string, array} but
-    got string'
+  want_error: 'object.remove: operand 2 must be one of {object, set, array} but got string'
   want_error_code: eval_type_error
   strict_error: true
diff --git a/test/cases/testdata/objectremove/test-objectremove-0295.yaml b/test/cases/testdata/objectremove/test-objectremove-0295.yaml
index e6bf64b323..2b1dce7e1b 100644
--- a/test/cases/testdata/objectremove/test-objectremove-0295.yaml
+++ b/test/cases/testdata/objectremove/test-objectremove-0295.yaml
@@ -12,7 +12,6 @@ cases:
     }
   note: objectremove/error invalid key param type boolean input
   query: data.generated.p = x
-  want_error: 'object.remove: operand 2 must be one of {object, string, array} but
-    got boolean'
+  want_error: 'object.remove: operand 2 must be one of {object, set, array} but got boolean'
   want_error_code: eval_type_error
   strict_error: true
diff --git a/test/cases/testdata/objectremove/test-objectremove-0296.yaml b/test/cases/testdata/objectremove/test-objectremove-0296.yaml
index d686ae8037..cf7811588e 100644
--- a/test/cases/testdata/objectremove/test-objectremove-0296.yaml
+++ b/test/cases/testdata/objectremove/test-objectremove-0296.yaml
@@ -12,7 +12,6 @@ cases:
     }
   note: objectremove/error invalid key param type number input
   query: data.generated.p = x
-  want_error: 'object.remove: operand 2 must be one of {object, string, array} but
-    got number'
+  want_error: 'object.remove: operand 2 must be one of {object, set, array} but got number'
   want_error_code: eval_type_error
   strict_error: true
diff --git a/test/cases/testdata/objectremove/test-objectremove-0297.yaml b/test/cases/testdata/objectremove/test-objectremove-0297.yaml
index 1e8ee4c06f..b23d47856c 100644
--- a/test/cases/testdata/objectremove/test-objectremove-0297.yaml
+++ b/test/cases/testdata/objectremove/test-objectremove-0297.yaml
@@ -12,7 +12,6 @@ cases:
     }
   note: objectremove/error invalid key param type nil input
   query: data.generated.p = x
-  want_error: 'object.remove: operand 2 must be one of {object, string, array} but
-    got null'
+  want_error: 'object.remove: operand 2 must be one of {object, set, array} but got null'
   want_error_code: eval_type_error
   strict_error: true
diff --git a/topdown/aggregates.go b/topdown/aggregates.go
index 63d60f56df..eba6db23dc 100644
--- a/topdown/aggregates.go
+++ b/topdown/aggregates.go
@@ -22,7 +22,7 @@ func builtinCount(a ast.Value) (ast.Value, error) {
 	case ast.String:
 		return ast.IntNumberTerm(len([]rune(a))).Value, nil
 	}
-	return nil, builtins.NewOperandTypeErr(1, a, "array", "object", "set")
+	return nil, builtins.NewOperandTypeErr(1, a, "array", "object", "set", "string")
 }
 
 func builtinSum(a ast.Value) (ast.Value, error) {
diff --git a/topdown/object.go b/topdown/object.go
index 1eb28073de..8d366ddad0 100644
--- a/topdown/object.go
+++ b/topdown/object.go
@@ -8,7 +8,6 @@ import (
 	"github.com/open-policy-agent/opa/ast"
 	"github.com/open-policy-agent/opa/internal/ref"
 	"github.com/open-policy-agent/opa/topdown/builtins"
-	"github.com/open-policy-agent/opa/types"
 )
 
 func builtinObjectUnion(_ BuiltinContext, operands []*ast.Term, iter func(*ast.Term) error) error {
@@ -148,7 +147,7 @@ func getObjectKeysParam(arrayOrSet ast.Value) (ast.Set, error) {
 			return nil
 		})
 	default:
-		return nil, builtins.NewOperandTypeErr(2, arrayOrSet, ast.TypeName(types.Object{}), ast.TypeName(types.S), ast.TypeName(types.Array{}))
+		return nil, builtins.NewOperandTypeErr(2, arrayOrSet, "object", "set", "array")
 	}
 
 	return keys, nil