diff --git a/hugolib/embedded_templates_test.go b/hugolib/embedded_templates_test.go
index 5d7d6dc23..f0fc9cfde 100644
--- a/hugolib/embedded_templates_test.go
+++ b/hugolib/embedded_templates_test.go
@@ -31,12 +31,16 @@ images=["siteimg1.jpg", "siteimg2.jpg"]
 
 	b.WithContent("mybundle/index.md", `---
 title: My Bundle
+date: 2021-02-26T18:02:00-01:00
+lastmod: 2021-05-22T19:25:00-01:00
 ---
 `)
 
 	b.WithContent("mypage.md", `---
 title: My Page
 images: ["pageimg1.jpg", "pageimg2.jpg"]
+date: 2021-02-26T18:02:00+01:00
+lastmod: 2021-05-22T19:25:00+01:00
 ---
 `)
 
@@ -62,16 +66,24 @@ title: My Site
 <meta property="og:title" content="My Bundle" />
 <meta property="og:url" content="https://example.org/mybundle/" />
 <meta property="og:image" content="https://example.org/mybundle/featured-sunset.jpg"/>
+<meta property="article:published_time" content="2021-02-26T18:02:00-01:00" />
+<meta property="article:modified_time" content="2021-05-22T19:25:00-01:00" />
 <meta itemprop="name" content="My Bundle">
 <meta itemprop="image" content="https://example.org/mybundle/featured-sunset.jpg">
+<meta itemprop="datePublished" content="2021-02-26T18:02:00-01:00" />
+<meta itemprop="dateModified" content="2021-05-22T19:25:00-01:00" />
 
 `)
 	b.AssertFileContent("public/mypage/index.html", `
 <meta name="twitter:image" content="https://example.org/pageimg1.jpg"/>
 <meta property="og:image" content="https://example.org/pageimg1.jpg" />
 <meta property="og:image" content="https://example.org/pageimg2.jpg" />
+<meta property="article:published_time" content="2021-02-26T18:02:00+01:00" />
+<meta property="article:modified_time" content="2021-05-22T19:25:00+01:00" />
 <meta itemprop="image" content="https://example.org/pageimg1.jpg">
-<meta itemprop="image" content="https://example.org/pageimg2.jpg">        
+<meta itemprop="image" content="https://example.org/pageimg2.jpg">
+<meta itemprop="datePublished" content="2021-02-26T18:02:00+01:00" />
+<meta itemprop="dateModified" content="2021-05-22T19:25:00+01:00" />
 `)
 	b.AssertFileContent("public/mysite/index.html", `
 <meta name="twitter:image" content="https://example.org/siteimg1.jpg"/>
diff --git a/tpl/tplimpl/embedded/templates.autogen.go b/tpl/tplimpl/embedded/templates.autogen.go
index cd706f8e1..b906f10d2 100644
--- a/tpl/tplimpl/embedded/templates.autogen.go
+++ b/tpl/tplimpl/embedded/templates.autogen.go
@@ -224,8 +224,8 @@ if (!doNotTrack) {
 {{- if .IsPage }}
 {{- $iso8601 := "2006-01-02T15:04:05-07:00" -}}
 <meta property="article:section" content="{{ .Section }}" />
-{{ with .PublishDate }}<meta property="article:published_time" content="{{ .Format $iso8601 }}" />{{ end }}
-{{ with .Lastmod }}<meta property="article:modified_time" content="{{ .Format $iso8601 }}" />{{ end }}
+{{ with .PublishDate }}<meta property="article:published_time" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end }}
+{{ with .Lastmod }}<meta property="article:modified_time" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end }}
 {{- end -}}
 
 {{- with .Params.audio }}<meta property="og:audio" content="{{ . }}" />{{ end }}
@@ -408,8 +408,8 @@ if (!doNotTrack) {
 
 {{- if .IsPage -}}
 {{- $iso8601 := "2006-01-02T15:04:05-07:00" -}}
-{{ with .PublishDate }}<meta itemprop="datePublished" content="{{ .Format $iso8601 }}" />{{ end}}
-{{ with .Lastmod }}<meta itemprop="dateModified" content="{{ .Format $iso8601 }}" />{{ end}}
+{{ with .PublishDate }}<meta itemprop="datePublished" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end}}
+{{ with .Lastmod }}<meta itemprop="dateModified" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end}}
 <meta itemprop="wordCount" content="{{ .WordCount }}">
 
 {{- with $.Params.images -}}
diff --git a/tpl/tplimpl/embedded/templates/opengraph.html b/tpl/tplimpl/embedded/templates/opengraph.html
index b0395ae2f..e3961524b 100644
--- a/tpl/tplimpl/embedded/templates/opengraph.html
+++ b/tpl/tplimpl/embedded/templates/opengraph.html
@@ -19,8 +19,8 @@
 {{- if .IsPage }}
 {{- $iso8601 := "2006-01-02T15:04:05-07:00" -}}
 <meta property="article:section" content="{{ .Section }}" />
-{{ with .PublishDate }}<meta property="article:published_time" content="{{ .Format $iso8601 }}" />{{ end }}
-{{ with .Lastmod }}<meta property="article:modified_time" content="{{ .Format $iso8601 }}" />{{ end }}
+{{ with .PublishDate }}<meta property="article:published_time" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end }}
+{{ with .Lastmod }}<meta property="article:modified_time" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end }}
 {{- end -}}
 
 {{- with .Params.audio }}<meta property="og:audio" content="{{ . }}" />{{ end }}
diff --git a/tpl/tplimpl/embedded/templates/schema.html b/tpl/tplimpl/embedded/templates/schema.html
index 772c6c2b1..20b477b59 100644
--- a/tpl/tplimpl/embedded/templates/schema.html
+++ b/tpl/tplimpl/embedded/templates/schema.html
@@ -3,8 +3,8 @@
 
 {{- if .IsPage -}}
 {{- $iso8601 := "2006-01-02T15:04:05-07:00" -}}
-{{ with .PublishDate }}<meta itemprop="datePublished" content="{{ .Format $iso8601 }}" />{{ end}}
-{{ with .Lastmod }}<meta itemprop="dateModified" content="{{ .Format $iso8601 }}" />{{ end}}
+{{ with .PublishDate }}<meta itemprop="datePublished" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end}}
+{{ with .Lastmod }}<meta itemprop="dateModified" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end}}
 <meta itemprop="wordCount" content="{{ .WordCount }}">
 
 {{- with $.Params.images -}}