diff --git a/baseline-refaster-rules/src/main/java/com/palantir/baseline/refaster/AssertjCollectionHasSameSizeAs.java b/baseline-refaster-rules/src/main/java/com/palantir/baseline/refaster/AssertjCollectionHasSameSizeAs.java
new file mode 100644
index 000000000..ede04f835
--- /dev/null
+++ b/baseline-refaster-rules/src/main/java/com/palantir/baseline/refaster/AssertjCollectionHasSameSizeAs.java
@@ -0,0 +1,44 @@
+/*
+ * (c) Copyright 2019 Palantir Technologies Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.palantir.baseline.refaster;
+
+import com.google.errorprone.refaster.ImportPolicy;
+import com.google.errorprone.refaster.annotation.AfterTemplate;
+import com.google.errorprone.refaster.annotation.BeforeTemplate;
+import com.google.errorprone.refaster.annotation.UseImportPolicy;
+import java.util.Collection;
+import org.assertj.core.api.IterableAssert;
+import org.assertj.core.api.ListAssert;
+
+public final class AssertjCollectionHasSameSizeAs<T, U> {
+
+    @BeforeTemplate
+    IterableAssert<T> before(IterableAssert<T> assertInProgress, Collection<U> expected) {
+        return assertInProgress.hasSize(expected.size());
+    }
+
+    @BeforeTemplate
+    ListAssert<T> before(ListAssert<T> assertInProgress, Collection<U> expected) {
+        return assertInProgress.hasSize(expected.size());
+    }
+
+    @AfterTemplate
+    @UseImportPolicy(ImportPolicy.STATIC_IMPORT_ALWAYS)
+    IterableAssert<T> after(IterableAssert<T> assertInProgress, Collection<U> expected) {
+        return assertInProgress.hasSameSizeAs(expected);
+    }
+}
diff --git a/baseline-refaster-rules/src/test/java/com/palantir/baseline/refaster/AssertjCollectionHasSameSizeAsTest.java b/baseline-refaster-rules/src/test/java/com/palantir/baseline/refaster/AssertjCollectionHasSameSizeAsTest.java
new file mode 100644
index 000000000..c91b8164c
--- /dev/null
+++ b/baseline-refaster-rules/src/test/java/com/palantir/baseline/refaster/AssertjCollectionHasSameSizeAsTest.java
@@ -0,0 +1,62 @@
+/*
+ * (c) Copyright 2019 Palantir Technologies Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.palantir.baseline.refaster;
+
+import static org.assertj.core.api.Assumptions.assumeThat;
+
+import org.junit.Test;
+
+public class AssertjCollectionHasSameSizeAsTest {
+
+    @Test
+    public void test() {
+        assumeThat(System.getProperty("java.specification.version"))
+                .describedAs("Refaster does not currently support fluent refactors on java 11")
+                .isEqualTo("1.8");
+        RefasterTestHelper
+                .forRefactoring(AssertjCollectionHasSameSizeAs.class)
+                .withInputLines(
+                        "Test",
+                        "import static org.assertj.core.api.Assertions.assertThat;",
+                        "import java.util.List;",
+                        "import java.util.Collection;",
+                        "public class Test {",
+                        "  void f(List<String> a, Collection<String> b, Iterable<String> c, List<String> target) {",
+                        "    assertThat(a).hasSize(target.size());",
+                        "    assertThat(b).hasSize(target.size());",
+                        "    assertThat(c).hasSize(target.size());",
+                        "    assertThat(a).describedAs(\"desc\").hasSize(target.size());",
+                        "    assertThat(b).describedAs(\"desc\").hasSize(target.size());",
+                        "    assertThat(c).describedAs(\"desc\").hasSize(target.size());",
+                        "  }",
+                        "}")
+                .hasOutputLines(
+                        "import static org.assertj.core.api.Assertions.assertThat;",
+                        "import java.util.List;",
+                        "import java.util.Collection;",
+                        "public class Test {",
+                        "  void f(List<String> a, Collection<String> b, Iterable<String> c, List<String> target) {",
+                        "    assertThat(a).hasSameSizeAs(target);",
+                        "    assertThat(b).hasSameSizeAs(target);",
+                        "    assertThat(c).hasSameSizeAs(target);",
+                        "    assertThat(a).describedAs(\"desc\").hasSameSizeAs(target);",
+                        "    assertThat(b).describedAs(\"desc\").hasSameSizeAs(target);",
+                        "    assertThat(c).describedAs(\"desc\").hasSameSizeAs(target);",
+                        "  }",
+                        "}");
+    }
+}
diff --git a/changelog/@unreleased/pr-900.v2.yml b/changelog/@unreleased/pr-900.v2.yml
new file mode 100644
index 000000000..72bc1d2c1
--- /dev/null
+++ b/changelog/@unreleased/pr-900.v2.yml
@@ -0,0 +1,5 @@
+type: improvement
+improvement:
+  description: refaster replacement for assertj hasSize(foo.size) -> hasSameSizeAs
+  links:
+  - https://github.com/palantir/gradle-baseline/pull/900