diff --git a/lib/ecto/adapters/myxql/connection.ex b/lib/ecto/adapters/myxql/connection.ex
index fb363b87..31b334e5 100644
--- a/lib/ecto/adapters/myxql/connection.ex
+++ b/lib/ecto/adapters/myxql/connection.ex
@@ -16,23 +16,28 @@ if Code.ensure_loaded?(MyXQL) do
 
     @impl true
     def prepare_execute(conn, name, sql, params, opts) do
+      ensure_list_params!(params)
       MyXQL.prepare_execute(conn, name, sql, params, opts)
     end
 
     @impl true
     def query(conn, sql, params, opts) do
+      ensure_list_params!(params)
       opts = Keyword.put_new(opts, :query_type, :binary_then_text)
       MyXQL.query(conn, sql, params, opts)
     end
 
     @impl true
     def query_many(conn, sql, params, opts) do
+      ensure_list_params!(params)
       opts = Keyword.put_new(opts, :query_type, :text)
       MyXQL.query_many(conn, sql, params, opts)
     end
 
     @impl true
     def execute(conn, query, params, opts) do
+      ensure_list_params!(params)
+
       case MyXQL.execute(conn, query, params, opts) do
         {:ok, _, result} -> {:ok, result}
         {:error, _} = error -> error
@@ -41,9 +46,16 @@ if Code.ensure_loaded?(MyXQL) do
 
     @impl true
     def stream(conn, sql, params, opts) do
+      ensure_list_params!(params)
       MyXQL.stream(conn, sql, params, opts)
     end
 
+    defp ensure_list_params!(params) do
+      unless is_list(params) do
+        raise ArgumentError, "expected params to be a list, got: #{inspect(params)}"
+      end
+    end
+
     @quotes ~w(" ' `)
 
     @impl true
diff --git a/lib/ecto/adapters/postgres/connection.ex b/lib/ecto/adapters/postgres/connection.ex
index 9b59e7f5..53a8af3e 100644
--- a/lib/ecto/adapters/postgres/connection.ex
+++ b/lib/ecto/adapters/postgres/connection.ex
@@ -99,6 +99,8 @@ if Code.ensure_loaded?(Postgrex) do
 
     @impl true
     def prepare_execute(conn, name, sql, params, opts) do
+      ensure_list_params!(params)
+
       case Postgrex.prepare_execute(conn, name, sql, params, opts) do
         {:error, %Postgrex.Error{postgres: %{pg_code: "22P02", message: message}} = error} ->
           context = """
@@ -121,6 +123,7 @@ if Code.ensure_loaded?(Postgrex) do
 
     @impl true
     def query(conn, sql, params, opts) do
+      ensure_list_params!(params)
       Postgrex.query(conn, sql, params, opts)
     end
 
@@ -131,6 +134,8 @@ if Code.ensure_loaded?(Postgrex) do
 
     @impl true
     def execute(conn, %{ref: ref} = query, params, opts) do
+      ensure_list_params!(params)
+
       case Postgrex.execute(conn, query, params, opts) do
         {:ok, %{ref: ^ref}, result} ->
           {:ok, result}
@@ -151,9 +156,16 @@ if Code.ensure_loaded?(Postgrex) do
 
     @impl true
     def stream(conn, sql, params, opts) do
+      ensure_list_params!(params)
       Postgrex.stream(conn, sql, params, opts)
     end
 
+    defp ensure_list_params!(params) do
+      unless is_list(params) do
+        raise ArgumentError, "expected params to be a list, got: #{inspect(params)}"
+      end
+    end
+
     @parent_as __MODULE__
     alias Ecto.Query.{BooleanExpr, ByExpr, JoinExpr, QueryExpr, WithExpr}
 
diff --git a/lib/ecto/adapters/sql.ex b/lib/ecto/adapters/sql.ex
index ba98643e..96ff0e59 100644
--- a/lib/ecto/adapters/sql.ex
+++ b/lib/ecto/adapters/sql.ex
@@ -102,6 +102,8 @@ defmodule Ecto.Adapters.SQL do
           optional(atom) => any
         }
 
+  @type query_params :: [term] | %{(atom | String.t()) => term}
+
   @doc false
   defmacro __using__(opts) do
     quote do
@@ -335,7 +337,7 @@ defmodule Ecto.Adapters.SQL do
 
   """
   @spec to_sql(:all | :update_all | :delete_all, Ecto.Repo.t(), Ecto.Queryable.t()) ::
-          {String.t(), [term]}
+          {String.t(), query_params}
   def to_sql(kind, repo, queryable) do
     case Ecto.Adapter.Queryable.prepare_query(kind, repo, queryable) do
       {{:cached, _update, _reset, {_id, cached}}, params} ->
@@ -510,7 +512,7 @@ defmodule Ecto.Adapters.SQL do
       [%{rows: [[42]], num_rows: 1}]
 
   """
-  @spec stream(Ecto.Repo.t(), String.t(), [term], Keyword.t()) :: Enum.t()
+  @spec stream(Ecto.Repo.t(), String.t(), query_params, Keyword.t()) :: Enum.t()
   def stream(repo, sql, params \\ [], opts \\ []) do
     repo
     |> Ecto.Adapter.lookup_meta()
@@ -520,7 +522,12 @@ defmodule Ecto.Adapters.SQL do
   @doc """
   Same as `query/4` but raises on invalid queries.
   """
-  @spec query!(pid() | Ecto.Repo.t() | Ecto.Adapter.adapter_meta(), iodata, [term], Keyword.t()) ::
+  @spec query!(
+          pid() | Ecto.Repo.t() | Ecto.Adapter.adapter_meta(),
+          iodata,
+          query_params,
+          Keyword.t()
+        ) ::
           query_result
   def query!(repo, sql, params \\ [], opts \\ []) do
     case query(repo, sql, params, opts) do
@@ -558,7 +565,12 @@ defmodule Ecto.Adapters.SQL do
       {:ok, %{rows: [[42]], num_rows: 1}}
 
   """
-  @spec query(pid() | Ecto.Repo.t() | Ecto.Adapter.adapter_meta(), iodata, [term], Keyword.t()) ::
+  @spec query(
+          pid() | Ecto.Repo.t() | Ecto.Adapter.adapter_meta(),
+          iodata,
+          query_params,
+          Keyword.t()
+        ) ::
           {:ok, query_result} | {:error, Exception.t()}
   def query(repo, sql, params \\ [], opts \\ [])
 
@@ -573,7 +585,12 @@ defmodule Ecto.Adapters.SQL do
   @doc """
   Same as `query_many/4` but raises on invalid queries.
   """
-  @spec query_many!(Ecto.Repo.t() | Ecto.Adapter.adapter_meta(), iodata, [term], Keyword.t()) ::
+  @spec query_many!(
+          Ecto.Repo.t() | Ecto.Adapter.adapter_meta(),
+          iodata,
+          query_params,
+          Keyword.t()
+        ) ::
           [query_result]
   def query_many!(repo, sql, params \\ [], opts \\ []) do
     case query_many(repo, sql, params, opts) do
@@ -614,7 +631,7 @@ defmodule Ecto.Adapters.SQL do
   @spec query_many(
           pid() | Ecto.Repo.t() | Ecto.Adapter.adapter_meta(),
           iodata,
-          [term],
+          query_params,
           Keyword.t()
         ) :: {:ok, [query_result]} | {:error, Exception.t()}
   def query_many(repo, sql, params \\ [], opts \\ [])
diff --git a/lib/ecto/adapters/tds/connection.ex b/lib/ecto/adapters/tds/connection.ex
index c0669e92..75c0d37f 100644
--- a/lib/ecto/adapters/tds/connection.ex
+++ b/lib/ecto/adapters/tds/connection.ex
@@ -79,6 +79,10 @@ if Code.ensure_loaded?(Tds) do
     def to_constraints(_, _opts), do: []
 
     def prepare_params(params) do
+      unless is_list(params) do
+        raise ArgumentError, "expected params to be a list, got: #{inspect(params)}"
+      end
+
       {params, _} =
         Enum.map_reduce(params, 1, fn param, acc ->
           case prepare_param(param) do