diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index c104059..fa26548 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -223,6 +223,12 @@
   g:inc_counter += 1
   assert_equal(2, g:inc_counter)
 
+  if has('float')
+    var f: float
+    f += 1
+    assert_equal(1.0, f)
+  endif
+
   $SOME_ENV_VAR ..= 'more'
   assert_equal('somemore', $SOME_ENV_VAR)
   CheckDefFailure(['$SOME_ENV_VAR += "more"'], 'E1051:')
diff --git a/src/version.c b/src/version.c
index 931a817..f2aae14 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3278,
+/**/
     3277,
 /**/
     3276,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index c5359fe..a487d00 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -7111,7 +7111,8 @@
 		if (
 #ifdef FEAT_FLOAT
 		    // If variable is float operation with number is OK.
-		    !(expected == &t_float && stacktype == &t_number) &&
+		    !(expected == &t_float && (stacktype == &t_number
+			    || stacktype == &t_number_bool)) &&
 #endif
 		    need_type(stacktype, expected, -1, 0, cctx,
 							 FALSE, FALSE) == FAIL)