diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -1124,7 +1124,9 @@
   ++PPBranchLevel;
   assert(PPBranchLevel >= 0 && PPBranchLevel <= (int)PPLevelBranchIndex.size());
   if (PPBranchLevel == (int)PPLevelBranchIndex.size()) {
-    PPLevelBranchIndex.push_back(0);
+    // If the first branch is unreachable, set the BranchIndex to 1.  This way
+    // the next branch it will be parsed if there is one.
+    PPLevelBranchIndex.push_back(Unreachable ? 1 : 0);
     PPLevelBranchCount.push_back(0);
   }
   PPChainBranchIndex.push(0);
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -5993,6 +5993,16 @@
                          ");\n"
                          "#else\n"
                          "#endif");
+
+  // Verify that indentation is correct when there is an `#if 0` with an
+  // `#else`.
+  verifyFormat("#if 0\n"
+               "{\n"
+               "#else\n"
+               "{\n"
+               "#endif\n"
+               "  x;\n"
+               "}");
 }
 
 TEST_F(FormatTest, GraciouslyHandleIncorrectPreprocessorConditions) {