diff --git a/src/mathed/InsetMathBox.cpp b/src/mathed/InsetMathBox.cpp
index 0872973dbf..2ee8d7c234 100644
--- a/src/mathed/InsetMathBox.cpp
+++ b/src/mathed/InsetMathBox.cpp
@@ -14,6 +14,7 @@
 #include "MathData.h"
 #include "MathStream.h"
 #include "MathStream.h"
+#include "LaTeXFeatures.h"
 #include "support/std_ostream.h"
 
 
@@ -74,4 +75,12 @@ void InsetMathBox::infoize(odocstream & os) const
 }
 
 
+void InsetMathBox::validate(LaTeXFeatures & features) const
+{
+	if (name_ == "tag" || name_ == "tag*")
+		features.require("amsmath");
+	cell(0).validate(features);
+}
+
+
 } // namespace lyx
diff --git a/src/mathed/InsetMathBox.h b/src/mathed/InsetMathBox.h
index b217dc57fa..38cc0afd03 100644
--- a/src/mathed/InsetMathBox.h
+++ b/src/mathed/InsetMathBox.h
@@ -40,6 +40,8 @@ public:
 	void normalize(NormalStream & ns) const;
 	///
 	void infoize(odocstream & os) const;
+	///
+	void validate(LaTeXFeatures & features) const;
 
 private:
 	virtual std::auto_ptr<Inset> doClone() const;
diff --git a/status.15x b/status.15x
index 673cea3ada..e7bc0b93b7 100644
--- a/status.15x
+++ b/status.15x
@@ -67,6 +67,8 @@ What's new
 
 - Allow to enter starred math commands like "\tag*" (bug 4584).
 
+- Load amsmath when \tag or \tag* is used (bug 4586).
+
 - Fix parameter input of the math commands \makebox and \framebox (bug 2461).
 
 - When cutting a selection do not leave a dangling paragraph (bug 3995).