diff --git a/core/src/main/java/org/teavm/backend/c/intrinsic/LongIntrinsic.java b/core/src/main/java/org/teavm/backend/c/intrinsic/LongIntrinsic.java
index 3b7ed7a21..9940f7402 100644
--- a/core/src/main/java/org/teavm/backend/c/intrinsic/LongIntrinsic.java
+++ b/core/src/main/java/org/teavm/backend/c/intrinsic/LongIntrinsic.java
@@ -27,6 +27,7 @@ public class LongIntrinsic implements Intrinsic {
         switch (method.getName()) {
             case "divideUnsigned":
             case "remainderUnsigned":
+            case "compareUnsigned":
                 return true;
             default:
                 return false;
@@ -42,6 +43,13 @@ public class LongIntrinsic implements Intrinsic {
             case "remainderUnsigned":
                 writeBinary(context, invocation, "%");
                 break;
+            case "compareUnsigned":
+                context.writer().print("teavm_compare_u64(");
+                context.emit(invocation.getArguments().get(0));
+                context.writer().print(", ");
+                context.emit(invocation.getArguments().get(1));
+                context.writer().print(")");
+                break;
         }
     }
 
diff --git a/core/src/main/resources/org/teavm/backend/c/core.h b/core/src/main/resources/org/teavm/backend/c/core.h
index c8bc01709..ee629c129 100644
--- a/core/src/main/resources/org/teavm/backend/c/core.h
+++ b/core/src/main/resources/org/teavm/backend/c/core.h
@@ -135,6 +135,9 @@ static inline int32_t teavm_compare_u32(int32_t a, int32_t b) {
 static inline int32_t teavm_compare_i64(int64_t a, int64_t b) {
     return a > b ? INT32_C(1) : a < b ? INT32_C(-1) : INT32_C(0);
 }
+static inline int32_t teavm_compare_u64(int64_t a, int64_t b) {
+    return (uint64_t) a > (uint64_t) b ? INT32_C(1) : (uint64_t) a < (uint64_t) b ? INT32_C(-1) : INT32_C(0);
+}
 static inline int32_t teavm_compare_float(float a, float b) {
     return a > b ? INT32_C(1) : a < b ? INT32_C(-1) : a == b ? INT32_C(0) : INT32_C(1);
 }