diff --git a/core/src/main/java/org/apache/calcite/sql/fun/SqlLibraryOperators.java b/core/src/main/java/org/apache/calcite/sql/fun/SqlLibraryOperators.java
index 28351847886..d58ae302d28 100644
--- a/core/src/main/java/org/apache/calcite/sql/fun/SqlLibraryOperators.java
+++ b/core/src/main/java/org/apache/calcite/sql/fun/SqlLibraryOperators.java
@@ -275,12 +275,18 @@ private static SqlCall transformConvert(SqlValidator validator, SqlCall call) {
   public static final SqlFunction LENGTH =
       SqlStdOperatorTable.CHAR_LENGTH.withName("LENGTH");
 
+  // Helper function for deriving types for the *PAD functions
+  private static RelDataType deriveTypePad(SqlOperatorBinding binding, RelDataType type) {
+    SqlTypeName result = SqlTypeUtil.isBinary(type) ? SqlTypeName.VARBINARY : SqlTypeName.VARCHAR;
+    return binding.getTypeFactory().createSqlType(result);
+  }
+
   /** The "LPAD(original_value, return_length[, pattern])" function. */
   @LibraryOperator(libraries = {BIG_QUERY, ORACLE})
   public static final SqlFunction LPAD =
       SqlBasicFunction.create(
           "LPAD",
-          ReturnTypes.ARG0_NULLABLE_VARYING,
+          ReturnTypes.ARG0.andThen(SqlLibraryOperators::deriveTypePad),
           OperandTypes.STRING_NUMERIC_OPTIONAL_STRING,
           SqlFunctionCategory.STRING);
 
@@ -289,7 +295,7 @@ private static SqlCall transformConvert(SqlValidator validator, SqlCall call) {
   public static final SqlFunction RPAD =
       SqlBasicFunction.create(
           "RPAD",
-          ReturnTypes.ARG0_NULLABLE_VARYING,
+          ReturnTypes.ARG0.andThen(SqlLibraryOperators::deriveTypePad),
           OperandTypes.STRING_NUMERIC_OPTIONAL_STRING,
           SqlFunctionCategory.STRING);
 
diff --git a/core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java b/core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java
index 71b80771ce9..b16a480203a 100644
--- a/core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java
+++ b/core/src/test/java/org/apache/calcite/test/RelOptRulesTest.java
@@ -262,6 +262,46 @@ private static boolean skipItem(RexNode expr) {
         .check();
   }
 
+  /**
+   * Test case for <a href="https://issues.apache.org/jira/browse/CALCITE-5989">[CALCITE-5989]
+   * Type inference for RPAD and LPAD functions (BIGQUERY) is incorrect</a>. */
+  @Test void testRpad() {
+    HepProgramBuilder builder = new HepProgramBuilder();
+    builder.addRuleClass(ReduceExpressionsRule.class);
+    HepPlanner hepPlanner = new HepPlanner(builder.build());
+    hepPlanner.addRule(CoreRules.PROJECT_REDUCE_EXPRESSIONS);
+
+    final String sql = "select RPAD('abc', 8, 'A')";
+    fixture()
+        .withFactory(
+            t -> t.withOperatorTable(opTab ->
+                SqlLibraryOperatorTableFactory.INSTANCE.getOperatorTable(
+                    SqlLibrary.BIG_QUERY))) // needed for RPAD function
+        .sql(sql)
+        .withPlanner(hepPlanner)
+        .check();
+  }
+
+  /**
+   * Test case for <a href="https://issues.apache.org/jira/browse/CALCITE-5989">[CALCITE-5989]
+   * Type inference for RPAD and LPAD functions (BIGQUERY) is incorrect</a>. */
+  @Test void testLpad() {
+    HepProgramBuilder builder = new HepProgramBuilder();
+    builder.addRuleClass(ReduceExpressionsRule.class);
+    HepPlanner hepPlanner = new HepPlanner(builder.build());
+    hepPlanner.addRule(CoreRules.PROJECT_REDUCE_EXPRESSIONS);
+
+    final String sql = "select LPAD('abc', 8, 'A')";
+    fixture()
+        .withFactory(
+            t -> t.withOperatorTable(opTab ->
+                SqlLibraryOperatorTableFactory.INSTANCE.getOperatorTable(
+                    SqlLibrary.BIG_QUERY))) // needed for LPAD function
+        .sql(sql)
+        .withPlanner(hepPlanner)
+        .check();
+  }
+
   /**
    * Test case for <a href="https://issues.apache.org/jira/browse/CALCITE-5971">[CALCITE-5971]
    * Add the RelRule to rewrite the bernoulli sample as Filter</a>. */
diff --git a/core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml b/core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml
index 65f8268c223..e529b3ae444 100644
--- a/core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml
+++ b/core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml
@@ -6221,6 +6221,23 @@ EnumerableLimitSort(sort0=[$0], dir0=[ASC], offset=[5], fetch=[10])
         EnumerableTableScan(table=[[CATALOG, SALES, EMP]])
       EnumerableProject(MGR=[$3])
         EnumerableTableScan(table=[[CATALOG, SALES, EMP]])
+]]>
+    </Resource>
+  </TestCase>
+  <TestCase name="testLpad">
+    <Resource name="sql">
+      <![CDATA[select LPAD('abc', 8, 'A')]]>
+    </Resource>
+    <Resource name="planBefore">
+      <![CDATA[
+LogicalProject(EXPR$0=[LPAD('abc', 8, 'A')])
+  LogicalValues(tuples=[[{ 0 }]])
+]]>
+    </Resource>
+    <Resource name="planAfter">
+      <![CDATA[
+LogicalProject(EXPR$0=['AAAAAabc':VARCHAR])
+  LogicalValues(tuples=[[{ 0 }]])
 ]]>
     </Resource>
   </TestCase>
@@ -12876,6 +12893,23 @@ LogicalProject(EXPR$0=[1])
       LogicalFilter(condition=[=($1, 'Charlie')])
         LogicalTableScan(table=[[CATALOG, SALES, DEPT]])
       LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+]]>
+    </Resource>
+  </TestCase>
+  <TestCase name="testRpad">
+    <Resource name="sql">
+      <![CDATA[select RPAD('abc', 8, 'A')]]>
+    </Resource>
+    <Resource name="planBefore">
+      <![CDATA[
+LogicalProject(EXPR$0=[RPAD('abc', 8, 'A')])
+  LogicalValues(tuples=[[{ 0 }]])
+]]>
+    </Resource>
+    <Resource name="planAfter">
+      <![CDATA[
+LogicalProject(EXPR$0=['abcAAAAA':VARCHAR])
+  LogicalValues(tuples=[[{ 0 }]])
 ]]>
     </Resource>
   </TestCase>
diff --git a/testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java b/testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java
index 0e23f666695..60bd95846d0 100644
--- a/testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java
+++ b/testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java
@@ -8225,20 +8225,20 @@ private void testCurrentDateFunc(Pair<String, Hook.Closeable> pair) {
   @Test void testLpadFunction() {
     final SqlOperatorFixture f = fixture().withLibrary(SqlLibrary.BIG_QUERY);
     f.setFor(SqlLibraryOperators.LPAD);
-    f.check("select lpad('12345', 8, 'a')", "VARCHAR(5) NOT NULL", "aaa12345");
-    f.checkString("lpad('12345', 8)", "   12345", "VARCHAR(5) NOT NULL");
-    f.checkString("lpad('12345', 8, 'ab')", "aba12345", "VARCHAR(5) NOT NULL");
-    f.checkString("lpad('12345', 3, 'a')", "123", "VARCHAR(5) NOT NULL");
+    f.check("select lpad('12345', 8, 'a')", "VARCHAR NOT NULL", "aaa12345");
+    f.checkString("lpad('12345', 8)", "   12345", "VARCHAR NOT NULL");
+    f.checkString("lpad('12345', 8, 'ab')", "aba12345", "VARCHAR NOT NULL");
+    f.checkString("lpad('12345', 3, 'a')", "123", "VARCHAR NOT NULL");
     f.checkFails("lpad('12345', -3, 'a')",
         "Second argument for LPAD/RPAD must not be negative", true);
     f.checkFails("lpad('12345', -3)",
         "Second argument for LPAD/RPAD must not be negative", true);
     f.checkFails("lpad('12345', 3, '')",
         "Third argument (pad pattern) for LPAD/RPAD must not be empty", true);
-    f.checkString("lpad(x'aa', 4, x'bb')", "bbbbbbaa", "VARBINARY(1) NOT NULL");
-    f.checkString("lpad(x'aa', 4)", "202020aa", "VARBINARY(1) NOT NULL");
-    f.checkString("lpad(x'aaaaaa', 2)", "aaaa", "VARBINARY(3) NOT NULL");
-    f.checkString("lpad(x'aaaaaa', 2, x'bb')", "aaaa", "VARBINARY(3) NOT NULL");
+    f.checkString("lpad(x'aa', 4, x'bb')", "bbbbbbaa", "VARBINARY NOT NULL");
+    f.checkString("lpad(x'aa', 4)", "202020aa", "VARBINARY NOT NULL");
+    f.checkString("lpad(x'aaaaaa', 2)", "aaaa", "VARBINARY NOT NULL");
+    f.checkString("lpad(x'aaaaaa', 2, x'bb')", "aaaa", "VARBINARY NOT NULL");
     f.checkFails("lpad(x'aa', -3, x'bb')",
         "Second argument for LPAD/RPAD must not be negative", true);
     f.checkFails("lpad(x'aa', -3)",
@@ -8250,10 +8250,10 @@ private void testCurrentDateFunc(Pair<String, Hook.Closeable> pair) {
   @Test void testRpadFunction() {
     final SqlOperatorFixture f = fixture().withLibrary(SqlLibrary.BIG_QUERY);
     f.setFor(SqlLibraryOperators.RPAD);
-    f.check("select rpad('12345', 8, 'a')", "VARCHAR(5) NOT NULL", "12345aaa");
-    f.checkString("rpad('12345', 8)", "12345   ", "VARCHAR(5) NOT NULL");
-    f.checkString("rpad('12345', 8, 'ab')", "12345aba", "VARCHAR(5) NOT NULL");
-    f.checkString("rpad('12345', 3, 'a')", "123", "VARCHAR(5) NOT NULL");
+    f.check("select rpad('12345', 8, 'a')", "VARCHAR NOT NULL", "12345aaa");
+    f.checkString("rpad('12345', 8)", "12345   ", "VARCHAR NOT NULL");
+    f.checkString("rpad('12345', 8, 'ab')", "12345aba", "VARCHAR NOT NULL");
+    f.checkString("rpad('12345', 3, 'a')", "123", "VARCHAR NOT NULL");
     f.checkFails("rpad('12345', -3, 'a')",
         "Second argument for LPAD/RPAD must not be negative", true);
     f.checkFails("rpad('12345', -3)",
@@ -8261,10 +8261,10 @@ private void testCurrentDateFunc(Pair<String, Hook.Closeable> pair) {
     f.checkFails("rpad('12345', 3, '')",
         "Third argument (pad pattern) for LPAD/RPAD must not be empty", true);
 
-    f.checkString("rpad(x'aa', 4, x'bb')", "aabbbbbb", "VARBINARY(1) NOT NULL");
-    f.checkString("rpad(x'aa', 4)", "aa202020", "VARBINARY(1) NOT NULL");
-    f.checkString("rpad(x'aaaaaa', 2)", "aaaa", "VARBINARY(3) NOT NULL");
-    f.checkString("rpad(x'aaaaaa', 2, x'bb')", "aaaa", "VARBINARY(3) NOT NULL");
+    f.checkString("rpad(x'aa', 4, x'bb')", "aabbbbbb", "VARBINARY NOT NULL");
+    f.checkString("rpad(x'aa', 4)", "aa202020", "VARBINARY NOT NULL");
+    f.checkString("rpad(x'aaaaaa', 2)", "aaaa", "VARBINARY NOT NULL");
+    f.checkString("rpad(x'aaaaaa', 2, x'bb')", "aaaa", "VARBINARY NOT NULL");
     f.checkFails("rpad(x'aa', -3, x'bb')",
         "Second argument for LPAD/RPAD must not be negative", true);
     f.checkFails("rpad(x'aa', -3)",