diff --git a/.rultor.yml b/.rultor.yml
index f06e65fd8e..9d86c1751a 100644
--- a/.rultor.yml
+++ b/.rultor.yml
@@ -41,7 +41,7 @@ install: |
   export JAVA_OPTS="-Xmx8g"
 merge:
   script: |
-    mvn clean install -Pqulice --errors -Dstyle.color=never
+    JAVA_OPTS="-Xmx8g" mvn clean install -Pqulice --errors -Dstyle.color=never
 release:
   pre: false
   script: |-
diff --git a/eo-runtime/src/test/java/org/eolang/MainTest.java b/eo-runtime/src/test/java/org/eolang/MainTest.java
index 136332fc29..b6bf6c3932 100644
--- a/eo-runtime/src/test/java/org/eolang/MainTest.java
+++ b/eo-runtime/src/test/java/org/eolang/MainTest.java
@@ -46,9 +46,9 @@ final class MainTest {
     @BeforeAll
     static void checkHeapSize() {
         MatcherAssert.assertThat(
-            "The maximum heap size is not big enough, some tests may fail",
+            "The maximum heap size is not big enough, some tests may fail, try to set JAVA_OPTS environment variable to '-Xmx8g'",
             Runtime.getRuntime().maxMemory(),
-            Matchers.greaterThan(8_000_000_000L)
+            Matchers.greaterThanOrEqualTo(8L * 1024 * 1024 * 1024)
         );
     }