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 && Line.Level < IndentForLevel.size())
+        IndentForLevel.resize(Line.Level + 1, -1);
+
       Indent = getIndent(Line.Level);
     }
     if (static_cast<int>(Indent) + Offset >= 0)
@@ -88,13 +94,13 @@
   /// level to the same indent.
   /// Note that \c nextLine must have been called before this method.
   void adjustToUnmodifiedLine(const AnnotatedLine &Line) {
-    unsigned LevelIndent = Line.First->OriginalColumn;
-    if (static_cast<int>(LevelIndent) - Offset >= 0)
-      LevelIndent -= Offset;
-    assert(Line.Level < IndentForLevel.size());
-    if ((!Line.First->is(tok::comment) || IndentForLevel[Line.Level] == -1) &&
-        !Line.InPPDirective) {
-      IndentForLevel[Line.Level] = LevelIndent;
+    if (!Line.InPPDirective) {
+      unsigned LevelIndent = Line.First->OriginalColumn;
+      if (static_cast<int>(LevelIndent) - Offset >= 0)
+        LevelIndent -= Offset;
+      assert(Line.Level < IndentForLevel.size());
+      if ((!Line.First->is(tok::comment) || IndentForLevel[Line.Level] == -1))
+        IndentForLevel[Line.Level] = LevelIndent;
     }
   }
 
@@ -148,6 +154,7 @@
   /// at \p IndentForLevel[l], or a value < 0 if the indent for
   /// that level is unknown.
   unsigned getIndent(unsigned Level) const {
+    assert(Level < IndentForLevel.size());
     if (IndentForLevel[Level] != -1)
       return IndentForLevel[Level];
     if (Level == 0)
@@ -160,6 +167,10 @@
   const unsigned AdditionalIndent;
 
   /// The indent in characters for each level.
+  /// It remembers the indent of previous lines (that are not PP directives) of
+  /// equal or lower levels. This is used to align formatted lines to the indent
+  /// of previous non-formatted lines. Think about the --lines parameter of
+  /// clang-format.
   SmallVector<int> IndentForLevel;
 
   /// Offset of the current line relative to the indent level.
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) {
@@ -617,6 +637,70 @@
          "namespace ns1 { namespace ns2 {\n"
          "}}";
   EXPECT_EQ(Code, format(Code, 0, 0));
+
+  Style = getLLVMStyle();
+  Style.FixNamespaceComments = false;
+  Code = "namespace ns {\n"
+         "#define REF(alias) alias alias_var;\n"
+         "}";
+  EXPECT_EQ(Code, format(Code, 51, 1));
+}
+
+TEST_F(FormatTestSelective, FormatMacroRegardlessOfPreviousIndent) {
+  // clang-format currently does not (or should not) take into account the
+  // indent of previous unformatted lines when formatting a PP directive.
+  // Technically speaking, LevelIndentTracker::IndentForLevel is only for non-PP
+  // lines. So these tests here check that the indent of previous non-PP lines
+  // do not affect the formatting. If this requirement changes, the tests here
+  // need to be adapted.
+  Style = getLLVMStyle();
+
+  Style.IndentPPDirectives = FormatStyle::PPDirectiveIndentStyle::PPDIS_None;
+  EXPECT_EQ("      class Foo {\n"
+            "            void test() {\n"
+            "    #ifdef 1\n"
+            "#define some\n" // Formatted line
+            "#endif\n"       // That this line is also formatted might be a bug.
+            "            }};", // Dito: Bug?
+            format("      class Foo {\n"
+                   "            void test() {\n"
+                   "    #ifdef 1\n"
+                   "                #define some\n" // format this line
+                   "         #endif\n"
+                   "    }};",
+                   75, 0));
+
+  Style.IndentPPDirectives =
+      FormatStyle::PPDirectiveIndentStyle::PPDIS_BeforeHash;
+  EXPECT_EQ("      class Foo {\n"
+            "            void test() {\n"
+            "    #ifdef 1\n"
+            "  #define some\n" // Formatted line
+            "         #endif\n"
+            "    }};",
+            format("      class Foo {\n"
+                   "            void test() {\n"
+                   "    #ifdef 1\n"
+                   "                #define some\n" // format this line
+                   "         #endif\n"
+                   "    }};",
+                   75, 0));
+
+  Style.IndentPPDirectives =
+      FormatStyle::PPDirectiveIndentStyle::PPDIS_AfterHash;
+  EXPECT_EQ("      class Foo {\n"
+            "            void test() {\n"
+            "    #ifdef 1\n"
+            "#  define some\n" // Formatted line
+            "#endif\n" // That this line is also formatted might be a bug.
+            "    }};",
+            format("      class Foo {\n"
+                   "            void test() {\n"
+                   "    #ifdef 1\n"
+                   "                #define some\n" // format this line
+                   "         #endif\n"
+                   "    }};",
+                   75, 0));
 }
 
 } // end namespace