diff --git a/CHANGELOG.md b/CHANGELOG.md
index 871aff8..d6c4767 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,4 +23,5 @@ Only accretive/fixative changes will be made from now on (Beta 1).
 
 The following changes have been committed to the **master** branch and will be in the next release:
 
+* Fix #24 by adding return type hints to `next.jdbc` functions.
 * Fix #22 by adding `next.jdbc.optional` with four map builders that omit `NULL` columns from the row hash maps.
diff --git a/src/next/jdbc.clj b/src/next/jdbc.clj
index deef04c..7c31036 100644
--- a/src/next/jdbc.clj
+++ b/src/next/jdbc.clj
@@ -87,6 +87,7 @@
   * `redshift` -- `com.amazon.redshift.jdbc.Driver` -- no default port
   * `sqlite` -- `org.sqlite.JDBC`
   * `sqlserver`, `mssql` -- `com.microsoft.sqlserver.jdbc.SQLServerDriver` -- `1433`"
+  ^javax.sql.DataSource
   [spec]
   (p/get-datasource spec))
 
@@ -105,10 +106,12 @@
 
   If you call `get-connection` on anything else, it will call `get-datasource`
   first to try to get a `DataSource`, and then call `get-connection` on that."
-  ([spec]
-   (p/get-connection spec {}))
-  ([spec opts]
-   (p/get-connection spec opts)))
+  (^java.sql.Connection
+    [spec]
+    (p/get-connection spec {}))
+  (^java.sql.Connection
+    [spec opts]
+    (p/get-connection spec opts)))
 
 (defn prepare
   "Given a connection to a database, and a vector containing SQL and any
@@ -123,10 +126,12 @@
 
   See the list of options above (in the namespace docstring) for what can
   be passed to prepare."
-  ([connection sql-params]
-   (p/prepare connection sql-params {}))
-  ([connection sql-params opts]
-   (p/prepare connection sql-params opts)))
+  (^java.sql.PreparedStatement
+    [connection sql-params]
+    (p/prepare connection sql-params {}))
+  (^java.sql.PreparedStatement
+    [connection sql-params opts]
+    (p/prepare connection sql-params opts)))
 
 (defn plan
   "General SQL execution function.
@@ -135,14 +140,17 @@
 
   Can be called on a `PreparedStatement`, a `Connection`, or something that can
   produce a `Connection` via a `DataSource`."
-  ([stmt]
-   (p/-execute stmt [] {}))
-  ([connectable sql-params]
-   (p/-execute connectable sql-params
-               {:next.jdbc/sql-params sql-params}))
-  ([connectable sql-params opts]
-   (p/-execute connectable sql-params
-               (assoc opts :next.jdbc/sql-params sql-params))))
+  (^clojure.lang.IReduceInit
+    [stmt]
+    (p/-execute stmt [] {}))
+  (^clojure.lang.IReduceInit
+    [connectable sql-params]
+    (p/-execute connectable sql-params
+                {:next.jdbc/sql-params sql-params}))
+  (^clojure.lang.IReduceInit
+    [connectable sql-params opts]
+    (p/-execute connectable sql-params
+                (assoc opts :next.jdbc/sql-params sql-params))))
 
 (defn execute!
   "General SQL execution function.
diff --git a/src/next/jdbc/protocols.clj b/src/next/jdbc/protocols.clj
index 9286069..6847de3 100644
--- a/src/next/jdbc/protocols.clj
+++ b/src/next/jdbc/protocols.clj
@@ -27,7 +27,7 @@
 
   Implementations are provided for `DataSource`, `PreparedStatement`, and
   `Object`, on the assumption that an `Object` can be turned into a `DataSource`."
-  (get-connection ^java.lang.AutoCloseable [this opts]
+  (get-connection ^java.sql.Connection [this opts]
     "Produce a new `java.sql.Connection` for use with `with-open`."))
 
 (defprotocol Executable
diff --git a/src/next/jdbc/quoted.clj b/src/next/jdbc/quoted.clj
index 1e5cdc7..598354a 100644
--- a/src/next/jdbc/quoted.clj
+++ b/src/next/jdbc/quoted.clj
@@ -6,6 +6,8 @@
   from Clojure data."
   (:require [clojure.string :as str]))
 
+(set! *warn-on-reflection* true)
+
 (defn ansi "ANSI \"quoting\"" [s] (str \" s \"))
 
 (defn mysql "MySQL `quoting`" [s] (str \` s \`))
diff --git a/src/next/jdbc/specs.clj b/src/next/jdbc/specs.clj
index 80cda5b..2c08ceb 100644
--- a/src/next/jdbc/specs.clj
+++ b/src/next/jdbc/specs.clj
@@ -19,6 +19,8 @@
   (:import (java.sql Connection PreparedStatement)
            (javax.sql DataSource)))
 
+(set! *warn-on-reflection* true)
+
 (s/def ::dbtype string?)
 (s/def ::dbname string?)
 (s/def ::classname string?)
diff --git a/src/next/jdbc/sql.clj b/src/next/jdbc/sql.clj
index ba7deb9..7958bbb 100644
--- a/src/next/jdbc/sql.clj
+++ b/src/next/jdbc/sql.clj
@@ -22,6 +22,8 @@
   (:require [clojure.string :as str]
             [next.jdbc :refer [execute! execute-one!]]))
 
+(set! *warn-on-reflection* true)
+
 (defn- by-keys
   "Given a hash map of column names and values and a clause type
   (`:set`, `:where`), return a vector of a SQL clause and its parameters.
diff --git a/test/next/jdbc/connection_test.clj b/test/next/jdbc/connection_test.clj
index e4809e6..4b36862 100644
--- a/test/next/jdbc/connection_test.clj
+++ b/test/next/jdbc/connection_test.clj
@@ -11,6 +11,8 @@
             [next.jdbc.connection :as c]
             [next.jdbc.protocols :as p]))
 
+(set! *warn-on-reflection* true)
+
 (def ^:private db-name "clojure_test")
 
 (deftest test-aliases-and-defaults
diff --git a/test/next/jdbc/optional_test.clj b/test/next/jdbc/optional_test.clj
index 8ba85fa..6d218d1 100644
--- a/test/next/jdbc/optional_test.clj
+++ b/test/next/jdbc/optional_test.clj
@@ -8,6 +8,8 @@
             [next.jdbc.protocols :as p]
             [next.jdbc.test-fixtures :refer [with-test-db ds]]))
 
+(set! *warn-on-reflection* true)
+
 (use-fixtures :once with-test-db)
 
 (deftest test-map-row-builder
diff --git a/test/next/jdbc/prepare_test.clj b/test/next/jdbc/prepare_test.clj
index daa6850..3703332 100644
--- a/test/next/jdbc/prepare_test.clj
+++ b/test/next/jdbc/prepare_test.clj
@@ -9,3 +9,5 @@
   actually work they way they're supposed to!"
   (:require [clojure.test :refer [deftest is testing]]
             [next.jdbc.prepare :refer :all]))
+
+(set! *warn-on-reflection* true)
diff --git a/test/next/jdbc/protocols_test.clj b/test/next/jdbc/protocols_test.clj
index b177726..b5be805 100644
--- a/test/next/jdbc/protocols_test.clj
+++ b/test/next/jdbc/protocols_test.clj
@@ -5,3 +5,5 @@
   at this level tho'..."
   (:require [clojure.test :refer [deftest is testing]]
             [next.jdbc.protocols :refer :all]))
+
+(set! *warn-on-reflection* true)
diff --git a/test/next/jdbc/quoted_test.clj b/test/next/jdbc/quoted_test.clj
index 0c52762..e62babb 100644
--- a/test/next/jdbc/quoted_test.clj
+++ b/test/next/jdbc/quoted_test.clj
@@ -7,6 +7,8 @@
             [next.jdbc.quoted :refer [ansi mysql sql-server oracle postgres
                                       schema]]))
 
+(set! *warn-on-reflection* true)
+
 (deftest basic-quoting
   (are [quote-fn quoted] (= (quote-fn "x") quoted)
     ansi       "\"x\""
diff --git a/test/next/jdbc/result_set_test.clj b/test/next/jdbc/result_set_test.clj
index 802007f..a01b7ac 100644
--- a/test/next/jdbc/result_set_test.clj
+++ b/test/next/jdbc/result_set_test.clj
@@ -14,6 +14,8 @@
             [next.jdbc.test-fixtures :refer [with-test-db ds]])
   (:import (java.sql ResultSet ResultSetMetaData)))
 
+(set! *warn-on-reflection* true)
+
 (use-fixtures :once with-test-db)
 
 (deftest test-datafy-nav
diff --git a/test/next/jdbc/specs_test.clj b/test/next/jdbc/specs_test.clj
index 19cdee5..56d92f4 100644
--- a/test/next/jdbc/specs_test.clj
+++ b/test/next/jdbc/specs_test.clj
@@ -7,3 +7,5 @@
   next.jdbc and next.jdbc.sql namespaces."
   (:require [clojure.test :refer [deftest is testing]]
             [next.jdbc.specs :refer :all]))
+
+(set! *warn-on-reflection* true)
diff --git a/test/next/jdbc/sql_test.clj b/test/next/jdbc/sql_test.clj
index fa43136..d211436 100644
--- a/test/next/jdbc/sql_test.clj
+++ b/test/next/jdbc/sql_test.clj
@@ -11,6 +11,8 @@
             [next.jdbc.test-fixtures
              :refer [with-test-db ds derby? sqlite?]]))
 
+(set! *warn-on-reflection* true)
+
 (use-fixtures :once with-test-db)
 
 (specs/instrument)
diff --git a/test/next/jdbc/test_fixtures.clj b/test/next/jdbc/test_fixtures.clj
index a304114..d4e19f8 100644
--- a/test/next/jdbc/test_fixtures.clj
+++ b/test/next/jdbc/test_fixtures.clj
@@ -5,6 +5,8 @@
   (:require [next.jdbc :as jdbc]
             [next.jdbc.sql :as sql]))
 
+(set! *warn-on-reflection* true)
+
 (def ^:private test-derby {:dbtype "derby" :dbname "clojure_test_derby" :create true})
 
 (def ^:private test-h2-mem {:dbtype "h2:mem" :dbname "clojure_test_h2_mem"})
diff --git a/test/next/jdbc/transaction_test.clj b/test/next/jdbc/transaction_test.clj
index 96b8395..c817ba3 100644
--- a/test/next/jdbc/transaction_test.clj
+++ b/test/next/jdbc/transaction_test.clj
@@ -4,3 +4,5 @@
   "Stub test namespace for transaction handling."
   (:require [clojure.test :refer [deftest is testing]]
             [next.jdbc.transaction :refer :all]))
+
+(set! *warn-on-reflection* true)
diff --git a/test/next/jdbc_test.clj b/test/next/jdbc_test.clj
index dd39527..ac0baff 100644
--- a/test/next/jdbc_test.clj
+++ b/test/next/jdbc_test.clj
@@ -10,6 +10,8 @@
             [next.jdbc.specs :as specs])
   (:import (java.sql ResultSet ResultSetMetaData)))
 
+(set! *warn-on-reflection* true)
+
 (use-fixtures :once with-test-db)
 
 (specs/instrument)