diff --git a/Sources/PostgreSQL/Database.swift b/Sources/PostgreSQL/Database.swift
index 8a51918..a1560dd 100644
--- a/Sources/PostgreSQL/Database.swift
+++ b/Sources/PostgreSQL/Database.swift
@@ -52,6 +52,10 @@ public class Database {
             defer {
                 for i in 0..<values.count {
                     let p = paramsValues[i]
+                    if p == nil {
+                        continue
+                    }
+                    
                     let mp = UnsafeMutablePointer(mutating: p)
                     mp?.deinitialize()
                     var i = 0
@@ -85,6 +89,13 @@ public class Database {
             .allocate(capacity: values.count)
 
         for i in 0..<values.count {
+            // PQexecParams converts nil pointer to NULL.
+            // see: https://www.postgresql.org/docs/9.1/static/libpq-exec.html
+            if values[i] == .null {
+                paramsValues[i] = nil
+                continue
+            }
+            
             var ch = values[i].string?.bytes ?? []
             ch.append(0)
 
diff --git a/Tests/PostgreSQLTests/PostgreSQLTests.swift b/Tests/PostgreSQLTests/PostgreSQLTests.swift
index 15ab3ba..525582b 100644
--- a/Tests/PostgreSQLTests/PostgreSQLTests.swift
+++ b/Tests/PostgreSQLTests/PostgreSQLTests.swift
@@ -70,6 +70,8 @@ class PostgreSQLTests: XCTestCase {
         do {
             try postgreSQL.execute("DROP TABLE IF EXISTS parameterization")
             try postgreSQL.execute("CREATE TABLE parameterization (d FLOAT4, i INT, s VARCHAR(16), u INT)")
+            
+            try postgreSQL.execute("INSERT INTO parameterization VALUES ($1, $2, $3, $4)", [.null, .null, "life".makeNode(), .null], on: nil)
 
             try postgreSQL.execute("INSERT INTO parameterization VALUES (3.14, NULL, 'pi', NULL)")
             try postgreSQL.execute("INSERT INTO parameterization VALUES (NULL, NULL, 'life', 42)")