diff --git a/docs/book/sql/where-having.md b/docs/book/sql/where-having.md
index 31573e4f..d77d15ec 100644
--- a/docs/book/sql/where-having.md
+++ b/docs/book/sql/where-having.md
@@ -394,6 +394,13 @@ class Expression implements
 }
 ```
 
+> **Note:** Unlike `Operator`, `Like`, `Between`, `In` and `IsNull`,
+> `Expression` does not accept a specification override. It always renders
+> the string given to its constructor or `setExpression()`, so calling
+> `setSpecification()` on an `Expression` (or `Predicate\Expression`) throws
+> `PhpDb\Sql\Exception\RuntimeException`. Call `setExpression()` to change
+> the SQL it renders.
+
 Expression parameters can be supplied in multiple ways:
 
 ```php title="Using Expression with various parameter types"
diff --git a/src/Sql/Exception/RuntimeException.php b/src/Sql/Exception/RuntimeException.php
index 51ecffc7..846c7347 100644
--- a/src/Sql/Exception/RuntimeException.php
+++ b/src/Sql/Exception/RuntimeException.php
@@ -34,6 +34,10 @@ class RuntimeException extends Exception\RuntimeException
         'A number of parameters (%d) was found'
             . ' that is not supported by this specification';
 
+    final public const string UNSUPPORTED_SPECIFICATION_OVERRIDE =
+        '%s renders its expression string and does not accept'
+            . ' a specification override; use setExpression() instead';
+
     public static function forReplacementMismatch(): self
     {
         return new self(self::REPLACEMENT_MISMATCH);
@@ -68,4 +72,9 @@ public static function forUnsupportedParameterCountOf(int $count): self
     {
         return new self(sprintf(self::UNSUPPORTED_PARAMETER_COUNT_OF, $count));
     }
+
+    public static function forUnsupportedSpecificationOverride(string $class): self
+    {
+        return new self(sprintf(self::UNSUPPORTED_SPECIFICATION_OVERRIDE, $class));
+    }
 }
diff --git a/src/Sql/Expression.php b/src/Sql/Expression.php
index 4450c39b..f44c916d 100644
--- a/src/Sql/Expression.php
+++ b/src/Sql/Expression.php
@@ -144,4 +144,16 @@ public function setParameters(
 
         return $this;
     }
+
+    /**
+     * Expression renders the string given to setExpression(), so a
+     * specification override would be silently ignored. Use setExpression().
+     *
+     * @throws Exception\RuntimeException
+     */
+    #[Override]
+    public function setSpecification(string $specification): static
+    {
+        throw Exception\RuntimeException::forUnsupportedSpecificationOverride(static::class);
+    }
 }
diff --git a/test/unit/Sql/Exception/RuntimeExceptionTest.php b/test/unit/Sql/Exception/RuntimeExceptionTest.php
index 57f965b2..88729bab 100644
--- a/test/unit/Sql/Exception/RuntimeExceptionTest.php
+++ b/test/unit/Sql/Exception/RuntimeExceptionTest.php
@@ -6,6 +6,7 @@
 
 use PhpDb\Exception\ExceptionInterface;
 use PhpDb\Sql\Exception\RuntimeException;
+use PhpDb\Sql\Expression;
 use PhpDb\Sql\SqlInterface;
 use PHPUnit\Framework\Attributes\CoversMethod;
 use PHPUnit\Framework\Attributes\DataProvider;
@@ -23,6 +24,7 @@
 #[CoversMethod(RuntimeException::class, 'forSubjectNotSqlInterface')]
 #[CoversMethod(RuntimeException::class, 'forUnsupportedParameterCount')]
 #[CoversMethod(RuntimeException::class, 'forUnsupportedParameterCountOf')]
+#[CoversMethod(RuntimeException::class, 'forUnsupportedSpecificationOverride')]
 final class RuntimeExceptionTest extends TestCase
 {
     /** @return array<string, array{string, list<string|int>, string}> */
@@ -64,6 +66,11 @@ public static function namedConstructorProvider(): array
                 [2],
                 RuntimeException::UNSUPPORTED_PARAMETER_COUNT_OF,
             ],
+            'unsupported specification override'   => [
+                'forUnsupportedSpecificationOverride',
+                [Expression::class],
+                RuntimeException::UNSUPPORTED_SPECIFICATION_OVERRIDE,
+            ],
         ];
     }
 
diff --git a/test/unit/Sql/ExpressionTest.php b/test/unit/Sql/ExpressionTest.php
index 2237448d..d454cdc6 100644
--- a/test/unit/Sql/ExpressionTest.php
+++ b/test/unit/Sql/ExpressionTest.php
@@ -18,6 +18,8 @@
 use PHPUnit\Framework\TestCase;
 use TypeError;
 
+use function sprintf;
+
 /**
  * This is a unit testing test case.
  * A unit here is a method, there will be at least one test per method
@@ -30,6 +32,8 @@
 #[CoversMethod(Expression::class, 'setParameters')]
 #[CoversMethod(Expression::class, 'getParameters')]
 #[CoversMethod(Expression::class, 'getExpressionData')]
+#[CoversMethod(Expression::class, 'setSpecification')]
+#[Group('unit')]
 final class ExpressionTest extends TestCase
 {
     /** @psalm-return array<array-key, array{0: mixed}> */
@@ -262,4 +266,17 @@ public function setParametersWrapsArrayInValuesArgument(): void
         static::assertCount(2, $data['values']);
         static::assertInstanceOf(Argument\Values::class, $data['values'][1]);
     }
+
+    #[Test]
+    public function setSpecificationIsRejectedInFavourOfSetExpression(): void
+    {
+        $expression = new Expression('LOWER(?) = ?', ['x', 'y']);
+
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage(
+            sprintf(RuntimeException::UNSUPPORTED_SPECIFICATION_OVERRIDE, Expression::class),
+        );
+
+        $expression->setSpecification('IGNORED %s %s');
+    }
 }
diff --git a/test/unit/Sql/Predicate/CustomSpecificationTest.php b/test/unit/Sql/Predicate/CustomSpecificationTest.php
new file mode 100644
index 00000000..bef7fa0f
--- /dev/null
+++ b/test/unit/Sql/Predicate/CustomSpecificationTest.php
@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpDbTest\Sql\Predicate;
+
+use PhpDb\Sql\AbstractExpression;
+use PhpDb\Sql\Predicate\Between;
+use PhpDb\Sql\Predicate\In;
+use PhpDb\Sql\Predicate\IsNull;
+use PhpDb\Sql\Predicate\Like;
+use PhpDb\Sql\Predicate\Operator;
+use PHPUnit\Framework\Attributes\CoversMethod;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Group;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Predicates built on AbstractExpression render a specification set through
+ * setSpecification() in place of their default format.
+ */
+#[CoversMethod(AbstractExpression::class, 'setSpecification')]
+#[CoversMethod(Between::class, 'getExpressionData')]
+#[CoversMethod(In::class, 'getExpressionData')]
+#[CoversMethod(IsNull::class, 'getExpressionData')]
+#[CoversMethod(Like::class, 'getExpressionData')]
+#[CoversMethod(Operator::class, 'getExpressionData')]
+#[Group('unit')]
+final class CustomSpecificationTest extends TestCase
+{
+    /** @return array<string, array{AbstractExpression, string}> */
+    public static function predicateProvider(): array
+    {
+        return [
+            'operator' => [new Operator('a', Operator::OPERATOR_EQUAL_TO, 1), '%1$s <=> %2$s'],
+            'like'     => [new Like('a', 'b%'), '%1$s SOUNDS LIKE %2$s'],
+            'between'  => [new Between('a', 1, 2), '%1$s BETWEEN SYMMETRIC %2$s AND %3$s'],
+            'is null'  => [new IsNull('a'), '%1$s IS UNKNOWN'],
+            'in'       => [new In('a', [1, 2]), '%s = ANY (%s)'],
+        ];
+    }
+
+    #[Test]
+    #[DataProvider('predicateProvider')]
+    public function rendersTheCustomSpecification(
+        AbstractExpression $predicate,
+        string $specification,
+    ): void {
+        $predicate->setSpecification($specification);
+
+        static::assertSame($specification, $predicate->getExpressionData()['spec']);
+    }
+}
diff --git a/test/unit/Sql/Predicate/ExpressionTest.php b/test/unit/Sql/Predicate/ExpressionTest.php
index f6bc50ab..590bffc2 100644
--- a/test/unit/Sql/Predicate/ExpressionTest.php
+++ b/test/unit/Sql/Predicate/ExpressionTest.php
@@ -9,12 +9,18 @@
 use PhpDb\Sql\Argument\Value;
 use PhpDb\Sql\ArgumentInterface;
 use PhpDb\Sql\ArgumentType;
+use PhpDb\Sql\Exception\RuntimeException;
 use PhpDb\Sql\Predicate\Expression;
 use PhpDb\Sql\Predicate\IsNull;
+use PHPUnit\Framework\Attributes\CoversMethod;
 use PHPUnit\Framework\Attributes\Group;
 use PHPUnit\Framework\Attributes\Test;
 use PHPUnit\Framework\TestCase;
 
+use function sprintf;
+
+#[CoversMethod(Expression::class, 'setSpecification')]
+#[Group('unit')]
 final class ExpressionTest extends TestCase
 {
     #[Test]
@@ -216,4 +222,17 @@ public function retrievingWherePartsReturnsSpecificationArrayOfLiteralAndParamet
         static::assertSame('foo.bar = %s AND id != %s', $expressionData['spec']);
         static::assertEquals([$parameter1, $parameter2], $expressionData['values']);
     }
+
+    #[Test]
+    public function setSpecificationIsRejectedInFavourOfSetExpression(): void
+    {
+        $expression = new Expression('LOWER(?) = ?', ['x', 'y']);
+
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessage(
+            sprintf(RuntimeException::UNSUPPORTED_SPECIFICATION_OVERRIDE, Expression::class),
+        );
+
+        $expression->setSpecification('IGNORED %s %s');
+    }
 }