diff -up vim74/runtime/syntax/yaml.vim.yamlsyntax vim74/runtime/syntax/yaml.vim
--- vim74/runtime/syntax/yaml.vim.yamlsyntax	2016-11-25 13:08:38.621772847 +0100
+++ vim74/runtime/syntax/yaml.vim	2016-11-25 15:04:38.170017620 +0100
@@ -103,14 +103,15 @@ execute 'syn match yamlPlainScalar conta
 syn match yamlMappingKeyStart '?\ze\s'
 syn match yamlMappingKeyStart '?' contained
 
-execute 'syn match yamlFlowMappingKey /'.s:ns_plain_in.'\ze\s*:/ contained '.
+execute 'syn match yamlFlowMappingKey /\%#=1'.s:ns_plain_in.'\%(\s\+'.s:ns_plain_in.'\)*\ze\s*:/ contained '.
             \'nextgroup=yamlKeyValueDelimiter'
 syn match yamlFlowMappingMerge /<<\ze\s*:/ contained nextgroup=yamlKeyValueDelimiter
 
 syn match yamlBlockCollectionItemStart '^\s*\zs-\%(\s\+-\)*\s' nextgroup=yamlBlockMappingKey,yamlBlockMappingMerge
-execute 'syn match yamlBlockMappingKey /^\s*\zs'.s:ns_plain_out.'\ze\s*:\%(\s\|$\)/ '.
+" Use the old regexp engine, the NFA engine doesn't like all the \@ items.
+execute 'syn match yamlBlockMappingKey /\%#=1^\s*\zs'.s:ns_plain_out.'\%(\s\+'.s:ns_plain_out.'\)*\ze\s*:\%(\s\|$\)/ '.
             \'nextgroup=yamlKeyValueDelimiter'
-execute 'syn match yamlBlockMappingKey /\s*\zs'.s:ns_plain_out.'\ze\s*:\%(\s\|$\)/ contained '.
+execute 'syn match yamlBlockMappingKey /\%#=1\s*\zs'.s:ns_plain_out.'\%(\s\+'.s:ns_plain_out.'\)*\ze\s*:\%(\s\|$\)/ contained '.
             \'nextgroup=yamlKeyValueDelimiter'
 syn match yamlBlockMappingMerge /^\s*\zs<<\ze:\%(\s\|$\)/ nextgroup=yamlKeyValueDelimiter
 syn match yamlBlockMappingMerge /<<\ze\s*:\%(\s\|$\)/ nextgroup=yamlKeyValueDelimiter contained