diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl b/automation/eclair_analysis/ECLAIR/deviations.ecl
index 9c67358d46..3a4d9ee3c0 100644
--- a/automation/eclair_analysis/ECLAIR/deviations.ecl
+++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
@@ -650,7 +650,8 @@ implements a set of functions that share the same names as their Standard Librar
 The implementation of these functions is available in source form, so the undefined, unspecified
 or implementation-defined behaviors contemplated by the C Standard do not apply.
 If some undefined or unspecified behavior does arise in the implementation, it
-falls under the jurisdiction of other MISRA rules."
+falls under the jurisdiction of other MISRA guidelines."
+-config=MC3A2.R21.6,reports+={deliberate, "any()"}
 -config=MC3A2.R21.9,reports+={deliberate, "any()"}
 -config=MC3A2.R21.10,reports+={deliberate, "any()"}
 -doc_end
diff --git a/automation/eclair_analysis/ECLAIR/monitored.ecl b/automation/eclair_analysis/ECLAIR/monitored.ecl
index ca2f5e3c7f..e2ad224d79 100644
--- a/automation/eclair_analysis/ECLAIR/monitored.ecl
+++ b/automation/eclair_analysis/ECLAIR/monitored.ecl
@@ -82,6 +82,7 @@
 -enable=MC3A2.R20.14
 -enable=MC3A2.R21.3
 -enable=MC3A2.R21.4
+-enable=MC3A2.R21.6
 -enable=MC3A2.R21.5
 -enable=MC3A2.R21.7
 -enable=MC3A2.R21.8
diff --git a/automation/eclair_analysis/ECLAIR/tagging.ecl b/automation/eclair_analysis/ECLAIR/tagging.ecl
index f9da5d5f4d..5bf214f480 100644
--- a/automation/eclair_analysis/ECLAIR/tagging.ecl
+++ b/automation/eclair_analysis/ECLAIR/tagging.ecl
@@ -93,6 +93,7 @@ MC3A2.R20.14||
 MC3A2.R21.3||
 MC3A2.R21.4||
 MC3A2.R21.5||
+MC3A2.R21.6||
 MC3A2.R21.7||
 MC3A2.R21.8||
 MC3A2.R21.9||
diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
index fe0b1e10a2..6cd8f48c91 100644
--- a/docs/misra/deviations.rst
+++ b/docs/misra/deviations.rst
@@ -587,7 +587,16 @@ Deviations related to MISRA C:2012 Rules:
        construct is deviated only in Translation Units that present a violation
        of the Rule due to uses of this macro.
      - Tagged as `deliberate` for ECLAIR.
-     
+
+   * - R21.6
+     - Xen does not use the input/output functions provided by the C
+       Standard Library, but provides in source form its own implementation,
+       therefore any unspecified or undefined behavior associated to the
+       functions provided by the Standard Library does not apply. Any such
+       behavior that may exist in such functions is therefore under the
+       jurisdiction of other MISRA C guidelines.
+     - Tagged as `deliberate` for ECLAIR.
+
    * - R21.9
      - Xen does not use the `bsearch` and `qsort` functions provided by the C
        Standard Library, but provides in source form its own implementation,