3 files changed, 19 insertions, 3 deletions
diff --git a/src/main/java/com/squareup/javapoet/MethodSpec.java b/src/main/java/com/squareup/javapoet/MethodSpec.java
index 2110f2e..1aa147f 100644
--- a/src/main/java/com/squareup/javapoet/MethodSpec.java
+++ b/src/main/java/com/squareup/javapoet/MethodSpec.java
@@ -287,7 +287,7 @@ public final class MethodSpec {
     private List<TypeVariableName> typeVariables = new ArrayList<>();
     private TypeName returnType;
     private final List<ParameterSpec> parameters = new ArrayList<>();
-    private final List<TypeName> exceptions = new ArrayList<>();
+    private final Set<TypeName> exceptions = new LinkedHashSet<>();
     private final CodeBlock.Builder code = CodeBlock.builder();
     private boolean varargs;
     private CodeBlock defaultValue;
diff --git a/src/main/java/com/squareup/javapoet/Util.java b/src/main/java/com/squareup/javapoet/Util.java
index 864598e..5b9f557 100644
--- a/src/main/java/com/squareup/javapoet/Util.java
+++ b/src/main/java/com/squareup/javapoet/Util.java
@@ -73,8 +73,8 @@ final class Util {
     if (!condition) throw new IllegalStateException(String.format(format, args));
   }
 
-  static <T> List<T> immutableList(List<T> list) {
-    return Collections.unmodifiableList(new ArrayList<>(list));
+  static <T> List<T> immutableList(Collection<T> collection) {
+    return Collections.unmodifiableList(new ArrayList<>(collection));
   }
 
   static <T> Set<T> immutableSet(Collection<T> set) {
diff --git a/src/test/java/com/squareup/javapoet/MethodSpecTest.java b/src/test/java/com/squareup/javapoet/MethodSpecTest.java
index a826d2d..2a6cbb2 100644
--- a/src/test/java/com/squareup/javapoet/MethodSpecTest.java
+++ b/src/test/java/com/squareup/javapoet/MethodSpecTest.java
@@ -21,9 +21,11 @@ import java.io.Closeable;
 import java.io.IOException;
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Target;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
 import java.util.concurrent.Callable;
+import java.util.concurrent.TimeoutException;
 import javax.lang.model.element.Element;
 import javax.lang.model.element.ExecutableElement;
 import javax.lang.model.element.Modifier;
@@ -206,4 +208,18 @@ public final class MethodSpecTest {
     assertThat(a.hashCode()).isEqualTo(b.hashCode());
   }
 
+  @Test public void duplicateExceptionsIgnored() {
+    ClassName ioException = ClassName.get(IOException.class);
+    ClassName timeoutException = ClassName.get(TimeoutException.class);
+    MethodSpec methodSpec = MethodSpec.methodBuilder("duplicateExceptions")
+      .addException(ioException)
+      .addException(timeoutException)
+      .addException(timeoutException)
+      .addException(ioException)
+      .build();
+    assertThat(methodSpec.exceptions).isEqualTo(Arrays.asList(ioException, timeoutException));
+    assertThat(methodSpec.toBuilder().addException(ioException).build().exceptions)
+      .isEqualTo(Arrays.asList(ioException, timeoutException));
+  }
+
 }