diff --git a/setup.py b/setup.py
index 26db763..c0bb513 100644
--- a/setup.py
+++ b/setup.py
@@ -1022,8 +1022,16 @@
             if db_setup_debug:
                 print("bsddb using BerkeleyDB lib:", db_ver, dblib)
                 print("bsddb lib dir:", dblib_dir, " inc dir:", db_incdir)
-            db_incs = [db_incdir]
             dblibs = [dblib]
+            # Only add the found library and include directories if they aren't
+            # already being searched. This avoids an explicit runtime library
+            # dependency.
+            if db_incdir in inc_dirs:
+                db_incs = None
+            else:
+                db_incs = [db_incdir]
+            if dblib_dir[0] in lib_dirs:
+                dblib_dir = None
         else:
             if db_setup_debug: print("db: no appropriate library found")
             db_incs = None
@@ -1134,6 +1142,9 @@
             # can end up with a bad search path order.
             if sqlite_incdir not in self.compiler.include_dirs:
                 include_dirs.append(sqlite_incdir)
+            # avoid a runtime library path for a system library dir
+            if sqlite_libdir and sqlite_libdir[0] in lib_dirs:
+                sqlite_libdir = None
             exts.append(Extension('_sqlite3', sqlite_srcs,
                                   define_macros=sqlite_defines,
                                   include_dirs=include_dirs,
@@ -1202,7 +1213,7 @@
                                 libraries = gdbm_libs)
                             break
                 elif cand == "bdb":
-                    if db_incs is not None:
+                    if dblibs:
                         if dbm_setup_debug: print("building dbm using bdb")
                         dbmext = Extension('_dbm', ['_dbmmodule.c'],
                                            library_dirs=dblib_dir,