diff --git a/kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/api/ProguardRules.kt b/kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/api/ProguardRules.kt
index bde3eaa..7b797f0 100644
--- a/kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/api/ProguardRules.kt
+++ b/kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/api/ProguardRules.kt
@@ -85,7 +85,11 @@ internal data class ProguardConfig(
       appendln("-if class $targetName")
       appendln("-keepclassmembers class ${targetClass.canonicalName} {")
       val allParams = targetConstructorParams.toMutableList()
-      val maskCount = (targetConstructorParams.size % 32) + 1
+      val maskCount = if (targetConstructorParams.isEmpty()) {
+        0
+      } else {
+        (targetConstructorParams.size + 31) / 32
+      }
       repeat(maskCount) {
         allParams += "int"
       }
diff --git a/kotlin/codegen/src/test/java/com/squareup/moshi/kotlin/codegen/JsonClassCodegenProcessorTest.kt b/kotlin/codegen/src/test/java/com/squareup/moshi/kotlin/codegen/JsonClassCodegenProcessorTest.kt
index 0de2fea..ee0c9ca 100644
--- a/kotlin/codegen/src/test/java/com/squareup/moshi/kotlin/codegen/JsonClassCodegenProcessorTest.kt
+++ b/kotlin/codegen/src/test/java/com/squareup/moshi/kotlin/codegen/JsonClassCodegenProcessorTest.kt
@@ -565,7 +565,7 @@ class JsonClassCodegenProcessorTest {
       -keepnames class kotlin.jvm.internal.DefaultConstructorMarker
       -if class testPackage.DefaultParams
       -keepclassmembers class testPackage.DefaultParams {
-          public synthetic <init>(java.lang.String,int,int,kotlin.jvm.internal.DefaultConstructorMarker);
+          public synthetic <init>(java.lang.String,int,kotlin.jvm.internal.DefaultConstructorMarker);
       }
     """.trimIndent())
 
@@ -583,7 +583,7 @@ class JsonClassCodegenProcessorTest {
       -keepnames class kotlin.jvm.internal.DefaultConstructorMarker
       -if class testPackage.Complex
       -keepclassmembers class testPackage.Complex {
-          public synthetic <init>(java.lang.String,java.util.List,java.lang.Object,int,int,int,int,kotlin.jvm.internal.DefaultConstructorMarker);
+          public synthetic <init>(java.lang.String,java.util.List,java.lang.Object,int,kotlin.jvm.internal.DefaultConstructorMarker);
       }
     """.trimIndent())