diff --git a/eo-runtime/src/main/java/org/eolang/Expect.java b/eo-runtime/src/main/java/org/eolang/Expect.java
index 9fd311f68d..98e5213399 100644
--- a/eo-runtime/src/main/java/org/eolang/Expect.java
+++ b/eo-runtime/src/main/java/org/eolang/Expect.java
@@ -81,7 +81,13 @@ public static Expect<Phi> at(final Phi phi, final String attr) {
     public <R> Expect<R> that(final Function<T, R> fun) {
         return new Expect<>(
             this.subject,
-            () -> fun.apply(this.sup.get())
+            () -> {
+                try {
+                    return fun.apply(this.sup.get());
+                } catch (final ExFailure ex) {
+                    throw new ExThat(ex.getMessage(), ex);
+                }
+            }
         );
     }
 
@@ -96,9 +102,19 @@ public Expect<T> otherwise(final String message) {
             () -> {
                 try {
                     return this.sup.get();
-                } catch (final ExFailure ex) {
+                } catch (final ExMust ex) {
+                    throw new ExFailure(
+                        String.format(
+                            "%s %s %s",
+                            this.subject,
+                            ex.getMessage(),
+                            message
+                        ),
+                        ex
+                    );
+                } catch (final ExThat ex) {
                     throw new ExFailure(
-                        String.format("%s %s %s", this.subject, ex.getMessage(), message),
+                        message,
                         ex
                     );
                 }
@@ -117,7 +133,7 @@ public Expect<T> must(final Function<T, Boolean> fun) {
             () -> {
                 final T ret = this.sup.get();
                 if (!fun.apply(ret)) {
-                    throw new ExFailure(
+                    throw new ExMust(
                         String.format("(%s)", ret)
                     );
                 }
@@ -135,4 +151,38 @@ public T it() {
         return this.sup.get();
     }
 
+    /**
+     * This exception is used to enhance the error message
+     * in the {@link Expect#otherwise(String)} method.
+     *
+     * @since 0.51
+     */
+    private static class ExMust extends ExFailure {
+        /**
+         * Ctor.
+         * @param cause Exception cause
+         * @param args Arguments for {@link String#format(String, Object...)}
+         */
+        ExMust(final String cause, final Object... args) {
+            super(String.format(cause, args));
+        }
+    }
+
+    /**
+     * This exception is used to enhance the error message
+     * in the {@link Expect#otherwise(String)} method.
+     *
+     * @since 0.51
+     */
+    private static class ExThat extends ExFailure {
+        /**
+         * Ctor.
+         * @param cause Exception cause
+         * @param args Arguments for {@link String#format(String, Object...)}
+         */
+        ExThat(final String cause, final Object... args) {
+            super(String.format(cause, args));
+        }
+    }
+
 }
diff --git a/eo-runtime/src/test/java/org/eolang/ExpectTest.java b/eo-runtime/src/test/java/org/eolang/ExpectTest.java
index 6793e27c66..b369d01dbe 100644
--- a/eo-runtime/src/test/java/org/eolang/ExpectTest.java
+++ b/eo-runtime/src/test/java/org/eolang/ExpectTest.java
@@ -36,9 +36,9 @@
 final class ExpectTest {
 
     @Test
-    void buildsAndChecks() {
+    void buildsAndChecksWithoutErrors() {
         MatcherAssert.assertThat(
-            "passes through and throws correctly",
+            "Passes checks",
             new Expect<>("something", () -> 42)
                 .must(i -> i > 0)
                 .otherwise("must be positive")
@@ -50,9 +50,9 @@ void buildsAndChecks() {
     }
 
     @Test
-    void failsWithCorrectTrace() {
+    void failsWithCorrectTraceWithOneError() {
         MatcherAssert.assertThat(
-            "error message is correct",
+            "Throw error in first 'must'. Error message is correct",
             Assertions.assertThrows(
                 ExFailure.class,
                 () -> new Expect<>("a number", () -> 42)
@@ -61,7 +61,65 @@ void failsWithCorrectTrace() {
                     .it(),
                 "fails on check"
             ).getMessage(),
-            Matchers.containsString("negative")
+            Matchers.equalTo("a number (42) must be negative")
+        );
+    }
+
+    @Test
+    void failsWithCorrectTraceWithTwoErrors() {
+        MatcherAssert.assertThat(
+            "Throw error in first 'must'. Not add error about second 'must'",
+            Assertions.assertThrows(
+                ExFailure.class,
+                () -> new Expect<>("a number", () -> 42.2)
+                    .must(i -> i < 0)
+                    .otherwise("must be negative")
+                    .must(i -> i % 1 == 0)
+                    .otherwise("must be an integer")
+                    .it(),
+                "fails only for first 'must'"
+            ).getMessage(),
+            Matchers.equalTo("a number (42.2) must be negative")
+        );
+    }
+
+    @Test
+    void failsWithCorrectTraceWithOneOkAndOneError() {
+        MatcherAssert.assertThat(
+            "Throw error in second 'must'. First 'must' passes check",
+            Assertions.assertThrows(
+                ExFailure.class,
+                () -> new Expect<>("a number", () -> 42.2)
+                    .must(i -> i > 0)
+                    .otherwise("must be positive")
+                    .must(i -> i % 1 == 0)
+                    .otherwise("must be an integer")
+                    .it(),
+                "fails on checking integer"
+            ).getMessage(),
+            Matchers.equalTo("a number (42.2) must be an integer")
+        );
+    }
+
+    @Test
+    void failsWithCorrectTraceWithExFailureInThat() {
+        MatcherAssert.assertThat(
+            "Take error message from 'otherwise', not from original error",
+            Assertions.assertThrows(
+                ExFailure.class,
+                () -> new Expect<>("something", () -> 42.2)
+                    .must(i -> i > 0)
+                    .otherwise("must be positive")
+                    .that(
+                        i -> {
+                            throw new ExFailure("some error");
+                        }
+                    )
+                    .otherwise("something went wrong")
+                    .it(),
+                "fails on 'that'"
+            ).getMessage(),
+            Matchers.equalTo("something went wrong")
         );
     }
 }