diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -74,6 +74,12 @@
                    : Line.Level * PPIndentWidth;
       Indent += AdditionalIndent;
     } else {
+      // When going to lower levels, forget previous higher levels so that we
+      // recompute future higher levels. But don't forget them if we enter a PP
+      // directive, since these do not terminate a code block.
+      if (!Line.InPPDirective)
+        IndentForLevel.resize(Line.Level + 1);
+
       Indent = getIndent(Line.Level);
     }
     if (static_cast<int>(Indent) + Offset >= 0)
@@ -910,6 +916,7 @@
       Tok->TotalLength += LengthA;
       A.Last = Tok;
     }
+    A.Level = B.Level;
   }
 
   const FormatStyle &Style;
diff --git a/clang/unittests/Format/FormatTestSelective.cpp b/clang/unittests/Format/FormatTestSelective.cpp
--- a/clang/unittests/Format/FormatTestSelective.cpp
+++ b/clang/unittests/Format/FormatTestSelective.cpp
@@ -528,6 +528,26 @@
             format("  int a;\n"
                    "void ffffff() {}",
                    11, 0));
+
+  // https://github.com/llvm/llvm-project/issues/59178
+  Style = getMozillaStyle();
+  EXPECT_EQ("int a()\n"
+            "{\n"
+            "return 0;\n"
+            "}\n"
+            "int b()\n"
+            "{\n"
+            "  return 42;\n"
+            "}",
+            format("int a()\n"
+                   "{\n"
+                   "return 0;\n"
+                   "}\n"
+                   "int b()\n"
+                   "{\n"
+                   "return 42;\n" // Format this line only
+                   "}",
+                   32, 0));
 }
 
 TEST_F(FormatTestSelective, UnderstandsTabs) {