Index: lib/Format/BreakableToken.cpp
===================================================================
--- lib/Format/BreakableToken.cpp
+++ lib/Format/BreakableToken.cpp
@@ -661,7 +661,6 @@
         else if (Prefix[i] == "//!")
           Prefix[i] = "//! ";
       }
-
       Tokens[i] = LineTok;
       Content[i] = Lines[i].substr(IndentPrefix.size());
       OriginalContentColumn[i] =
@@ -796,10 +795,13 @@
     } else {
       // This is the first line for the current token, but no reflow with the
       // previous token is necessary. However, we still may need to adjust the
-      // start column.
+      // start column. Note that ContentColumn[LineIndex] is the expected
+      // content column after a possible update to the prefix, hence the prefix
+      // length change is included.
       unsigned LineColumn =
           ContentColumn[LineIndex] -
-          (Content[LineIndex].data() - Lines[LineIndex].data());
+          (Content[LineIndex].data() - Lines[LineIndex].data()) +
+          (OriginalPrefix[LineIndex].size() - Prefix[LineIndex].size());
       if (tokenAt(LineIndex).OriginalColumn != LineColumn) {
         Whitespaces.replaceWhitespace(*Tokens[LineIndex],
                                       /*Newlines=*/1,
@@ -813,7 +815,8 @@
                                         /*InPPDirective=*/false);
       }
     }
-  } else if (OriginalPrefix[LineIndex] != Prefix[LineIndex]) {
+  }
+  if (OriginalPrefix[LineIndex] != Prefix[LineIndex]) {
     // This is not the first line of the token. Adjust the prefix if necessary.
 
     // Take care of the space possibly introduced after a decoration.
Index: unittests/Format/FormatTest.cpp
===================================================================
--- unittests/Format/FormatTest.cpp
+++ unittests/Format/FormatTest.cpp
@@ -1371,6 +1371,25 @@
             format("//Even if it makes the line exceed the column limit",
                    getLLVMStyleWithColumns(51)));
   EXPECT_EQ("//--But not here", format("//--But not here", getLLVMStyle()));
+  EXPECT_EQ("/// line 1\n"
+            "// add leading whitespace",
+            format("/// line 1\n"
+                   "//add leading whitespace",
+                   getLLVMStyleWithColumns(30)));
+  EXPECT_EQ("/// line 1\n"
+            "/// line 2\n"
+            "//! line 3\n"
+            "//! line 4\n"
+            "//! line 5\n"
+            "// line 6\n"
+            "// line 7",
+            format("///line 1\n"
+                   "///line 2\n"
+                   "//! line 3\n"
+                   "//!line 4\n"
+                   "//!line 5\n"
+                   "// line 6\n"
+                   "//line 7", getLLVMStyleWithColumns(20)));
 
   EXPECT_EQ("// aa bb cc dd",
             format("// aa bb             cc dd                   ",