diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index c867226..2a3021a 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,8 @@
+2019-03-22  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/bits/stl_algobase.h (__lg): Do arithmetic on type int to
+	avoid -Wconversion warnings.
+
 2019-03-21  Thomas Rodgers  <trodgers@redhat.com>
 	
 	* include/Makefile.am (std_header): Add ${std_srcdir}/execution.
diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
index 2b69e65..3b11394 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -1018,27 +1018,27 @@
   //  Precondition: __n > 0.
   inline _GLIBCXX_CONSTEXPR int
   __lg(int __n)
-  { return sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }
+  { return (int)sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }
 
   inline _GLIBCXX_CONSTEXPR unsigned
   __lg(unsigned __n)
-  { return sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }
+  { return (int)sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }
 
   inline _GLIBCXX_CONSTEXPR long
   __lg(long __n)
-  { return sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
+  { return (int)sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
 
   inline _GLIBCXX_CONSTEXPR unsigned long
   __lg(unsigned long __n)
-  { return sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
+  { return (int)sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
 
   inline _GLIBCXX_CONSTEXPR long long
   __lg(long long __n)
-  { return sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
+  { return (int)sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
 
   inline _GLIBCXX_CONSTEXPR unsigned long long
   __lg(unsigned long long __n)
-  { return sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
+  { return (int)sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
 
 _GLIBCXX_BEGIN_NAMESPACE_ALGO