diff --git a/toolchain/lex/tokenized_buffer.cpp b/toolchain/lex/tokenized_buffer.cpp
index cd62253ba8b3..9a1cf17aba87 100644
--- a/toolchain/lex/tokenized_buffer.cpp
+++ b/toolchain/lex/tokenized_buffer.cpp
@@ -300,8 +300,18 @@ class [[clang::internal_linkage]] TokenizedBuffer::Lexer {
   auto LexHorizontalWhitespace(llvm::StringRef& source_text) -> void {
     CARBON_DCHECK(source_text.front() == ' ' || source_text.front() == '\t');
     NoteWhitespace();
-    ++current_column_;
-    source_text = source_text.drop_front();
+    // Handle adjacent whitespace quickly. This comes up frequently for example
+    // due to indentation. We don't expect *huge* runs, so just use a scalar
+    // loop. While still scalar, this avoids repeated table dispatch and marking
+    // whitespace. We use `ssize_t` in the loop for performance.
+    ssize_t ws_count = 1;
+    ssize_t size = source_text.size();
+    while (ws_count < size &&
+           (source_text[ws_count] == ' ' || source_text[ws_count] == '\t')) {
+      ++ws_count;
+    }
+    current_column_ += ws_count;
+    source_text = source_text.drop_front(ws_count);
   }
 
   auto LexVerticalWhitespace(llvm::StringRef& source_text) -> void {