diff --git a/google/api_core/rest_helpers.py b/google/api_core/rest_helpers.py
index 23fb614f..a78822f1 100644
--- a/google/api_core/rest_helpers.py
+++ b/google/api_core/rest_helpers.py
@@ -18,8 +18,8 @@
 import operator
 
 
-def flatten_query_params(obj):
-    """Flatten a nested dict into a list of (name,value) tuples.
+def flatten_query_params(obj, strict=False):
+    """Flatten a dict into a list of (name,value) tuples.
 
     The result is suitable for setting query params on an http request.
 
@@ -28,9 +28,10 @@ def flatten_query_params(obj):
         >>> obj = {'a':
         ...         {'b':
         ...           {'c': ['x', 'y', 'z']} },
-        ...      'd': 'uvw', }
-        >>> flatten_query_params(obj)
-        [('a.b.c', 'x'), ('a.b.c', 'y'), ('a.b.c', 'z'), ('d', 'uvw')]
+        ...      'd': 'uvw',
+        ...      'e': True, }
+        >>> flatten_query_params(obj, strict=True)
+        [('a.b.c', 'x'), ('a.b.c', 'y'), ('a.b.c', 'z'), ('d', 'uvw'), ('e', 'true')]
 
     Note that, as described in
     https://github.com/googleapis/googleapis/blob/48d9fb8c8e287c472af500221c6450ecd45d7d39/google/api/http.proto#L117,
@@ -38,7 +39,9 @@ def flatten_query_params(obj):
     This is enforced in this function.
 
     Args:
-      obj: a nested dictionary (from json), or None
+      obj: a possibly nested dictionary (from json), or None
+      strict: a bool, defaulting to False, to enforce that all values in the
+              result tuples be strings and, if boolean, lower-cased.
 
     Returns: a list of tuples, with each tuple having a (possibly) multi-part name
       and a scalar value.
@@ -51,17 +54,17 @@ def flatten_query_params(obj):
     if obj is not None and not isinstance(obj, dict):
         raise TypeError("flatten_query_params must be called with dict object")
 
-    return _flatten(obj, key_path=[])
+    return _flatten(obj, key_path=[], strict=strict)
 
 
-def _flatten(obj, key_path):
+def _flatten(obj, key_path, strict=False):
     if obj is None:
         return []
     if isinstance(obj, dict):
-        return _flatten_dict(obj, key_path=key_path)
+        return _flatten_dict(obj, key_path=key_path, strict=strict)
     if isinstance(obj, list):
-        return _flatten_list(obj, key_path=key_path)
-    return _flatten_value(obj, key_path=key_path)
+        return _flatten_list(obj, key_path=key_path, strict=strict)
+    return _flatten_value(obj, key_path=key_path, strict=strict)
 
 
 def _is_primitive_value(obj):
@@ -74,21 +77,33 @@ def _is_primitive_value(obj):
     return True
 
 
-def _flatten_value(obj, key_path):
-    return [(".".join(key_path), obj)]
+def _flatten_value(obj, key_path, strict=False):
+    return [(".".join(key_path), _canonicalize(obj, strict=strict))]
 
 
-def _flatten_dict(obj, key_path):
-    items = (_flatten(value, key_path=key_path + [key]) for key, value in obj.items())
+def _flatten_dict(obj, key_path, strict=False):
+    items = (
+        _flatten(value, key_path=key_path + [key], strict=strict)
+        for key, value in obj.items()
+    )
     return functools.reduce(operator.concat, items, [])
 
 
-def _flatten_list(elems, key_path):
+def _flatten_list(elems, key_path, strict=False):
     # Only lists of scalar values are supported.
     # The name (key_path) is repeated for each value.
     items = (
-        _flatten_value(elem, key_path=key_path)
+        _flatten_value(elem, key_path=key_path, strict=strict)
         for elem in elems
         if _is_primitive_value(elem)
     )
     return functools.reduce(operator.concat, items, [])
+
+
+def _canonicalize(obj, strict=False):
+    if strict:
+        value = str(obj)
+        if isinstance(obj, bool):
+            value = value.lower()
+        return value
+    return obj
diff --git a/tests/unit/test_rest_helpers.py b/tests/unit/test_rest_helpers.py
index 5932fa55..ff1a43f0 100644
--- a/tests/unit/test_rest_helpers.py
+++ b/tests/unit/test_rest_helpers.py
@@ -36,9 +36,26 @@ def test_flatten_empty_dict():
 
 
 def test_flatten_simple_dict():
-    assert rest_helpers.flatten_query_params({"a": "abc", "b": "def"}) == [
+    obj = {"a": "abc", "b": "def", "c": True, "d": False, "e": 10, "f": -3.76}
+    assert rest_helpers.flatten_query_params(obj) == [
         ("a", "abc"),
         ("b", "def"),
+        ("c", True),
+        ("d", False),
+        ("e", 10),
+        ("f", -3.76),
+    ]
+
+
+def test_flatten_simple_dict_strict():
+    obj = {"a": "abc", "b": "def", "c": True, "d": False, "e": 10, "f": -3.76}
+    assert rest_helpers.flatten_query_params(obj, strict=True) == [
+        ("a", "abc"),
+        ("b", "def"),
+        ("c", "true"),
+        ("d", "false"),
+        ("e", "10"),
+        ("f", "-3.76"),
     ]