diff --git a/libc/src/__support/arg_list.h b/libc/src/__support/arg_list.h
--- a/libc/src/__support/arg_list.h
+++ b/libc/src/__support/arg_list.h
@@ -12,6 +12,7 @@
 #include "src/__support/common.h"
 
 #include <stdarg.h>
+#include <stddef.h>
 
 namespace __llvm_libc {
 namespace internal {
@@ -32,6 +33,42 @@
   template <class T> LIBC_INLINE T next_var() { return va_arg(vlist, T); }
 };
 
+// Used for testing things that use an ArgList.
+class MockArgList {
+  size_t arg_counter = 0;
+
+public:
+  LIBC_INLINE MockArgList() = default;
+  LIBC_INLINE MockArgList(va_list vlist) {
+    // Copy the vlist to suppress "unused parameter" warnings.
+    va_list copy_vlist;
+    va_copy(copy_vlist, vlist);
+    va_end(copy_vlist);
+  }
+  LIBC_INLINE MockArgList(MockArgList &other) {
+    arg_counter = other.arg_counter;
+  }
+  LIBC_INLINE ~MockArgList() = default;
+
+  LIBC_INLINE MockArgList &operator=(MockArgList &rhs) {
+    arg_counter = rhs.arg_counter;
+    return *this;
+  }
+
+  template <class T> LIBC_INLINE T next_var() {
+    ++arg_counter;
+    return T(arg_counter);
+  }
+
+  size_t read_count() const { return arg_counter; }
+};
+
+#ifndef LIBC_COPT_MOCK_ARG_LIST
+using ArgProvider = ArgList;
+#else  // not defined LIBC_COPT_MOCK_ARG_LIST
+using ArgProvider = MockArgList;
+#endif // LIBC_COPT_MOCK_ARG_LIST
+
 } // namespace internal
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fprintf.cpp b/libc/src/stdio/fprintf.cpp
--- a/libc/src/stdio/fprintf.cpp
+++ b/libc/src/stdio/fprintf.cpp
@@ -21,9 +21,9 @@
                     ...)) {
   va_list vlist;
   va_start(vlist, format);
-  internal::ArgList args(vlist); // This holder class allows for easier copying
-                                 // and pointer semantics, as well as handling
-                                 // destruction automatically.
+  internal::ArgProvider args(vlist); // This holder class allows for easier
+                                     // copying and pointer semantics, as well
+                                     // as handling destruction automatically.
   va_end(vlist);
   int ret_val = printf_core::vfprintf_internal(stream, format, args);
   return ret_val;
diff --git a/libc/src/stdio/fscanf.cpp b/libc/src/stdio/fscanf.cpp
--- a/libc/src/stdio/fscanf.cpp
+++ b/libc/src/stdio/fscanf.cpp
@@ -22,9 +22,9 @@
                     ...)) {
   va_list vlist;
   va_start(vlist, format);
-  internal::ArgList args(vlist); // This holder class allows for easier copying
-                                 // and pointer semantics, as well as handling
-                                 // destruction automatically.
+  internal::ArgProvider args(vlist); // This holder class allows for easier
+                                     // copying and pointer semantics, as well
+                                     // as handling destruction automatically.
   va_end(vlist);
   int ret_val = scanf_core::vfscanf_internal(stream, format, args);
   // This is done to avoid including stdio.h in the internals. On most systems
diff --git a/libc/src/stdio/printf.cpp b/libc/src/stdio/printf.cpp
--- a/libc/src/stdio/printf.cpp
+++ b/libc/src/stdio/printf.cpp
@@ -19,9 +19,9 @@
 LLVM_LIBC_FUNCTION(int, printf, (const char *__restrict format, ...)) {
   va_list vlist;
   va_start(vlist, format);
-  internal::ArgList args(vlist); // This holder class allows for easier copying
-                                 // and pointer semantics, as well as handling
-                                 // destruction automatically.
+  internal::ArgProvider args(vlist); // This holder class allows for easier
+                                     // copying and pointer semantics, as well
+                                     // as handling destruction automatically.
   va_end(vlist);
   int ret_val = printf_core::vfprintf_internal(
       reinterpret_cast<::FILE *>(__llvm_libc::stdout), format, args);
diff --git a/libc/src/stdio/printf_core/parser.h b/libc/src/stdio/printf_core/parser.h
--- a/libc/src/stdio/printf_core/parser.h
+++ b/libc/src/stdio/printf_core/parser.h
@@ -24,20 +24,20 @@
   const char *__restrict str;
 
   size_t cur_pos = 0;
-  internal::ArgList args_cur;
+  internal::ArgProvider args_cur;
 
 #ifndef LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
   // args_start stores the start of the va_args, which is allows getting the
   // value of arguments that have already been passed. args_index is tracked so
   // that we know which argument args_cur is on.
-  internal::ArgList args_start;
+  internal::ArgProvider args_start;
   size_t args_index = 1;
 
   // Defined in printf_config.h
   static constexpr size_t DESC_ARR_LEN = LIBC_COPT_PRINTF_INDEX_ARR_LEN;
 
-  // desc_arr stores the sizes of the variables in the ArgList. This is used in
-  // index mode to reduce repeated string parsing. The sizes are stored as
+  // desc_arr stores the sizes of the variables in the ArgProvider. This is used
+  // in index mode to reduce repeated string parsing. The sizes are stored as
   // TypeDesc objects, which store the size as well as minimal type information.
   // This is necessary because some systems separate the floating point and
   // integer values in va_args.
@@ -49,10 +49,12 @@
 
 public:
 #ifndef LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
-  LIBC_INLINE Parser(const char *__restrict new_str, internal::ArgList &args)
+  LIBC_INLINE Parser(const char *__restrict new_str,
+                     internal::ArgProvider &args)
       : str(new_str), args_cur(args), args_start(args) {}
 #else
-  LIBC_INLINE Parser(const char *__restrict new_str, internal::ArgList &args)
+  LIBC_INLINE Parser(const char *__restrict new_str,
+                     internal::ArgProvider &args)
       : str(new_str), args_cur(args) {}
 #endif // LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 
@@ -111,7 +113,7 @@
     return get_next_arg_value<T>();
   }
 
-  // the ArgList can only return the next item in the list. This function is
+  // the ArgProvider can only return the next item in the list. This function is
   // used in index mode when the item that needs to be read is not the next one.
   // It moves cur_args to the index requested so the the appropriate value may
   // be read. This may involve parsing the format string, and is in the worst
diff --git a/libc/src/stdio/printf_core/printf_main.h b/libc/src/stdio/printf_core/printf_main.h
--- a/libc/src/stdio/printf_core/printf_main.h
+++ b/libc/src/stdio/printf_core/printf_main.h
@@ -18,7 +18,7 @@
 namespace printf_core {
 
 int printf_main(Writer *writer, const char *__restrict str,
-                internal::ArgList &args);
+                internal::ArgProvider &args);
 
 } // namespace printf_core
 } // namespace __llvm_libc
diff --git a/libc/src/stdio/printf_core/printf_main.cpp b/libc/src/stdio/printf_core/printf_main.cpp
--- a/libc/src/stdio/printf_core/printf_main.cpp
+++ b/libc/src/stdio/printf_core/printf_main.cpp
@@ -20,7 +20,7 @@
 namespace printf_core {
 
 int printf_main(Writer *writer, const char *__restrict str,
-                internal::ArgList &args) {
+                internal::ArgProvider &args) {
   Parser parser(str, args);
   int result = 0;
   for (FormatSection cur_section = parser.get_next_section();
diff --git a/libc/src/stdio/printf_core/vfprintf_internal.h b/libc/src/stdio/printf_core/vfprintf_internal.h
--- a/libc/src/stdio/printf_core/vfprintf_internal.h
+++ b/libc/src/stdio/printf_core/vfprintf_internal.h
@@ -17,7 +17,7 @@
 namespace printf_core {
 
 int vfprintf_internal(::FILE *__restrict stream, const char *__restrict format,
-                      internal::ArgList &args);
+                      internal::ArgProvider &args);
 } // namespace printf_core
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/printf_core/vfprintf_internal.cpp b/libc/src/stdio/printf_core/vfprintf_internal.cpp
--- a/libc/src/stdio/printf_core/vfprintf_internal.cpp
+++ b/libc/src/stdio/printf_core/vfprintf_internal.cpp
@@ -19,7 +19,7 @@
 namespace printf_core {
 
 int vfprintf_internal(::FILE *__restrict stream, const char *__restrict format,
-                      internal::ArgList &args) {
+                      internal::ArgProvider &args) {
   FileWriter file_writer(stream);
   printf_core::Writer writer(reinterpret_cast<void *>(&file_writer),
                              printf_core::FileWriter::write_str,
diff --git a/libc/src/stdio/scanf.cpp b/libc/src/stdio/scanf.cpp
--- a/libc/src/stdio/scanf.cpp
+++ b/libc/src/stdio/scanf.cpp
@@ -20,9 +20,9 @@
 LLVM_LIBC_FUNCTION(int, scanf, (const char *__restrict format, ...)) {
   va_list vlist;
   va_start(vlist, format);
-  internal::ArgList args(vlist); // This holder class allows for easier copying
-                                 // and pointer semantics, as well as handling
-                                 // destruction automatically.
+  internal::ArgProvider args(vlist); // This holder class allows for easier
+                                     // copying and pointer semantics, as well
+                                     // as handling destruction automatically.
   va_end(vlist);
   int ret_val = scanf_core::vfscanf_internal(
       reinterpret_cast<::FILE *>(__llvm_libc::stdin), format, args);
diff --git a/libc/src/stdio/scanf_core/parser.h b/libc/src/stdio/scanf_core/parser.h
--- a/libc/src/stdio/scanf_core/parser.h
+++ b/libc/src/stdio/scanf_core/parser.h
@@ -23,22 +23,24 @@
   const char *__restrict str;
 
   size_t cur_pos = 0;
-  internal::ArgList args_cur;
+  internal::ArgProvider args_cur;
 
 #ifndef LIBC_COPT_SCANF_DISABLE_INDEX_MODE
   // args_start stores the start of the va_args, which is used when a previous
   // argument is needed. In that case, we have to read the arguments from the
   // beginning since they don't support reading backwards.
-  internal::ArgList args_start;
+  internal::ArgProvider args_start;
   size_t args_index = 1;
 #endif // LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
 public:
 #ifndef LIBC_COPT_SCANF_DISABLE_INDEX_MODE
-  LIBC_INLINE Parser(const char *__restrict new_str, internal::ArgList &args)
+  LIBC_INLINE Parser(const char *__restrict new_str,
+                     internal::ArgProvider &args)
       : str(new_str), args_cur(args), args_start(args) {}
 #else
-  LIBC_INLINE Parser(const char *__restrict new_str, internal::ArgList &args)
+  LIBC_INLINE Parser(const char *__restrict new_str,
+                     internal::ArgProvider &args)
       : str(new_str), args_cur(args) {}
 #endif // LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
@@ -84,7 +86,7 @@
     return get_next_arg_value<T>();
   }
 
-  // the ArgList can only return the next item in the list. This function is
+  // the ArgProvider can only return the next item in the list. This function is
   // used in index mode when the item that needs to be read is not the next one.
   // It moves cur_args to the index requested so the the appropriate value may
   // be read. This may involve parsing the format string, and is in the worst
diff --git a/libc/src/stdio/scanf_core/scanf_main.h b/libc/src/stdio/scanf_core/scanf_main.h
--- a/libc/src/stdio/scanf_core/scanf_main.h
+++ b/libc/src/stdio/scanf_core/scanf_main.h
@@ -18,7 +18,7 @@
 namespace scanf_core {
 
 int scanf_main(Reader *reader, const char *__restrict str,
-               internal::ArgList &args);
+               internal::ArgProvider &args);
 
 } // namespace scanf_core
 } // namespace __llvm_libc
diff --git a/libc/src/stdio/scanf_core/scanf_main.cpp b/libc/src/stdio/scanf_core/scanf_main.cpp
--- a/libc/src/stdio/scanf_core/scanf_main.cpp
+++ b/libc/src/stdio/scanf_core/scanf_main.cpp
@@ -20,7 +20,7 @@
 namespace scanf_core {
 
 int scanf_main(Reader *reader, const char *__restrict str,
-               internal::ArgList &args) {
+               internal::ArgProvider &args) {
   Parser parser(str, args);
   int ret_val = READ_OK;
   int conversions = 0;
diff --git a/libc/src/stdio/scanf_core/vfscanf_internal.h b/libc/src/stdio/scanf_core/vfscanf_internal.h
--- a/libc/src/stdio/scanf_core/vfscanf_internal.h
+++ b/libc/src/stdio/scanf_core/vfscanf_internal.h
@@ -17,7 +17,7 @@
 namespace scanf_core {
 
 int vfscanf_internal(::FILE *__restrict stream, const char *__restrict format,
-                     internal::ArgList &args);
+                     internal::ArgProvider &args);
 } // namespace scanf_core
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/scanf_core/vfscanf_internal.cpp b/libc/src/stdio/scanf_core/vfscanf_internal.cpp
--- a/libc/src/stdio/scanf_core/vfscanf_internal.cpp
+++ b/libc/src/stdio/scanf_core/vfscanf_internal.cpp
@@ -19,7 +19,7 @@
 namespace scanf_core {
 
 int vfscanf_internal(::FILE *__restrict stream, const char *__restrict format,
-                     internal::ArgList &args) {
+                     internal::ArgProvider &args) {
   FileReader file_reader(stream);
   scanf_core::Reader reader(&file_reader);
   return scanf_core::scanf_main(&reader, format, args);
diff --git a/libc/src/stdio/snprintf.cpp b/libc/src/stdio/snprintf.cpp
--- a/libc/src/stdio/snprintf.cpp
+++ b/libc/src/stdio/snprintf.cpp
@@ -23,9 +23,9 @@
                     const char *__restrict format, ...)) {
   va_list vlist;
   va_start(vlist, format);
-  internal::ArgList args(vlist); // This holder class allows for easier copying
-                                 // and pointer semantics, as well as handling
-                                 // destruction automatically.
+  internal::ArgProvider args(vlist); // This holder class allows for easier
+                                     // copying and pointer semantics, as well
+                                     // as handling destruction automatically.
   va_end(vlist);
   printf_core::StringWriter str_writer(buffer, (buffsz > 0 ? buffsz - 1 : 0));
   printf_core::Writer writer(reinterpret_cast<void *>(&str_writer),
diff --git a/libc/src/stdio/sprintf.cpp b/libc/src/stdio/sprintf.cpp
--- a/libc/src/stdio/sprintf.cpp
+++ b/libc/src/stdio/sprintf.cpp
@@ -22,9 +22,9 @@
                     ...)) {
   va_list vlist;
   va_start(vlist, format);
-  internal::ArgList args(vlist); // This holder class allows for easier copying
-                                 // and pointer semantics, as well as handling
-                                 // destruction automatically.
+  internal::ArgProvider args(vlist); // This holder class allows for easier
+                                     // copying and pointer semantics, as well
+                                     // as handling destruction automatically.
   va_end(vlist);
   printf_core::StringWriter str_writer(buffer);
   printf_core::Writer writer(reinterpret_cast<void *>(&str_writer),
diff --git a/libc/src/stdio/sscanf.cpp b/libc/src/stdio/sscanf.cpp
--- a/libc/src/stdio/sscanf.cpp
+++ b/libc/src/stdio/sscanf.cpp
@@ -23,9 +23,9 @@
                     const char *__restrict format, ...)) {
   va_list vlist;
   va_start(vlist, format);
-  internal::ArgList args(vlist); // This holder class allows for easier copying
-                                 // and pointer semantics, as well as handling
-                                 // destruction automatically.
+  internal::ArgProvider args(vlist); // This holder class allows for easier
+                                     // copying and pointer semantics, as well
+                                     // as handling destruction automatically.
   va_end(vlist);
   scanf_core::StringReader string_reader(buffer);
   scanf_core::Reader reader(&string_reader);
diff --git a/libc/test/src/__support/arg_list_test.cpp b/libc/test/src/__support/arg_list_test.cpp
--- a/libc/test/src/__support/arg_list_test.cpp
+++ b/libc/test/src/__support/arg_list_test.cpp
@@ -13,7 +13,7 @@
 int get_nth_int(int n, ...) {
   va_list vlist;
   va_start(vlist, n);
-  __llvm_libc::internal::ArgList v(vlist);
+  __llvm_libc::internal::ArgProvider v(vlist);
   va_end(vlist);
 
   for (int i = 0; i < n; ++i) {
@@ -29,10 +29,10 @@
 int sum_two_nums(int first, int second, ...) {
   va_list vlist;
   va_start(vlist, second);
-  __llvm_libc::internal::ArgList v1(vlist);
+  __llvm_libc::internal::ArgProvider v1(vlist);
   va_end(vlist);
 
-  __llvm_libc::internal::ArgList v2 = v1;
+  __llvm_libc::internal::ArgProvider v2 = v1;
 
   int first_val;
   for (int i = 0; i < first; ++i) {
diff --git a/libc/test/src/stdio/printf_core/parser_test.cpp b/libc/test/src/stdio/printf_core/parser_test.cpp
--- a/libc/test/src/stdio/printf_core/parser_test.cpp
+++ b/libc/test/src/stdio/printf_core/parser_test.cpp
@@ -21,7 +21,7 @@
 void init(const char *__restrict str, ...) {
   va_list vlist;
   va_start(vlist, str);
-  __llvm_libc::internal::ArgList v(vlist);
+  __llvm_libc::internal::ArgProvider v(vlist);
   va_end(vlist);
 
   __llvm_libc::printf_core::Parser parser(str, v);
@@ -31,7 +31,7 @@
               const char *__restrict str, ...) {
   va_list vlist;
   va_start(vlist, str);
-  __llvm_libc::internal::ArgList v(vlist);
+  __llvm_libc::internal::ArgProvider v(vlist);
   va_end(vlist);
 
   __llvm_libc::printf_core::Parser parser(str, v);
diff --git a/libc/test/src/stdio/scanf_core/parser_test.cpp b/libc/test/src/stdio/scanf_core/parser_test.cpp
--- a/libc/test/src/stdio/scanf_core/parser_test.cpp
+++ b/libc/test/src/stdio/scanf_core/parser_test.cpp
@@ -22,7 +22,7 @@
 void init(const char *__restrict str, ...) {
   va_list vlist;
   va_start(vlist, str);
-  __llvm_libc::internal::ArgList v(vlist);
+  __llvm_libc::internal::ArgProvider v(vlist);
   va_end(vlist);
 
   __llvm_libc::scanf_core::Parser parser(str, v);
@@ -32,7 +32,7 @@
               const char *__restrict str, ...) {
   va_list vlist;
   va_start(vlist, str);
-  __llvm_libc::internal::ArgList v(vlist);
+  __llvm_libc::internal::ArgProvider v(vlist);
   va_end(vlist);
 
   __llvm_libc::scanf_core::Parser parser(str, v);