diff --git a/format.cc b/format.cc
index 77fd1fd5..b7138985 100644
--- a/format.cc
+++ b/format.cc
@@ -393,7 +393,7 @@ void fmt::BasicWriter<Char>::FormatDouble(
   case 0:
     type = 'g';
     break;
-  case 'e': case 'f': case 'g':
+  case 'e': case 'f': case 'g': case 'a':
     break;
   case 'F':
 #ifdef _MSC_VER
@@ -401,7 +401,7 @@ void fmt::BasicWriter<Char>::FormatDouble(
     type = 'f';
 #endif
     // Fall through.
-  case 'E': case 'G':
+  case 'E': case 'G': case 'A':
     upper = true;
     break;
   default:
@@ -707,17 +707,11 @@ void fmt::BasicWriter<Char>::PrintfParser::Format(
       spec.width_ = 0;
       ParseFlags(spec, s, *arg);
 
-      /*
-      if (*s == '#') {
-        if (arg.type > LAST_NUMERIC_TYPE)
-          ReportError(s, "format specifier '#' requires numeric argument");
-        spec.flags_ |= HASH_FLAG;
-        ++s;
-      }*/
-
       // Parse width and zero flag.
-      if (*s < '0' || *s > '9')
+      if (*s < '0' || *s > '9') {
+        // TODO: parse '*' width
         break;
+      }
       spec.width_ = internal::ParseNonnegativeInt(s, error);
     }
     // Fall through.
diff --git a/test/format-test.cc b/test/format-test.cc
index 6a9db1a0..7d4b12e0 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -1201,7 +1201,7 @@ TEST(FormatterTest, FormatFloat) {
 }
 
 TEST(FormatterTest, FormatDouble) {
-  CheckUnknownTypes(1.2, "eEfFgG", "double");
+  CheckUnknownTypes(1.2, "eEfFgGaA", "double");
   EXPECT_EQ("0", str(Format("{0:}") << 0.0));
   EXPECT_EQ("0.000000", str(Format("{0:f}") << 0.0));
   EXPECT_EQ("392.65", str(Format("{0:}") << 392.65));
@@ -1215,6 +1215,8 @@ TEST(FormatterTest, FormatDouble) {
   SPrintf(buffer, "%E", 392.65);
   EXPECT_EQ(buffer, str(Format("{0:E}") << 392.65));
   EXPECT_EQ("+0000392.6", str(Format("{0:+010.4g}") << 392.65));
+  EXPECT_EQ("-0x1.5p+5", str(Format("{:a}") << -42.0));
+  EXPECT_EQ("-0X1.5P+5", str(Format("{:A}") << -42.0));
 }
 
 TEST(FormatterTest, FormatNaN) {
diff --git a/test/printf-test.cc b/test/printf-test.cc
index d6a3f3ab..35878e39 100644
--- a/test/printf-test.cc
+++ b/test/printf-test.cc
@@ -210,9 +210,8 @@ TEST(PrintfTest, HashFlag) {
   EXPECT_PRINTF("-42.0000", "%#g", -42.0);
   EXPECT_PRINTF("-42.0000", "%#G", -42.0);
 
-  // TODO
-  //EXPECT_PRINTF("-0x1.5p+5", "%#a", -42.0);
-  //EXPECT_PRINTF("-0x1.5A+5", "%#A", -42.0);
+  EXPECT_PRINTF("0x1.p+4", "%#a", 16.0);
+  EXPECT_PRINTF("0X1.P+4", "%#A", 16.0);
 
   // '#' flag is ignored for non-numeric types.
   EXPECT_PRINTF("x", "%#c", 'x');