diff --git a/requirements/edx-sandbox/py35-constraints.txt b/requirements/edx-sandbox/py35-constraints.txt
index c8cb6ea2b7a5..23ff7b627b19 100644
--- a/requirements/edx-sandbox/py35-constraints.txt
+++ b/requirements/edx-sandbox/py35-constraints.txt
@@ -22,6 +22,8 @@ sympy<1.7.0             # sympy 1.7.0 drops support for Python 3.5
 
 markupsafe<2.0.0        # markupsafe 2.0.0 requires Python >= 3.6
 
+nltk<3.6.3        		# nltk 3.6.3 drops support for Python 3.5
+
 cryptography<3.3        # cryptography 3.3 has dropped python3.5 support.
 PyJWT[crypto]<2.0.0     # PYJWT[crypto]==2.0.1 requires cryptography>=3.3.1
 social-auth-core<4.0.0  # social-auth-core>=4.0.0 requires PYJWT>=2.0.0
diff --git a/requirements/edx-sandbox/py35.in b/requirements/edx-sandbox/py35.in
index d1087cfd8472..e4d1a2184b80 100644
--- a/requirements/edx-sandbox/py35.in
+++ b/requirements/edx-sandbox/py35.in
@@ -21,7 +21,7 @@ cryptography                        # Implementations of assorted cryptography a
 lxml                                # XML parser
 matplotlib==2.2.4                   # 2D plotting library
 networkx==2.2                       # Utilities for creating, manipulating, and studying network graphs
-nltk                                # Natural language processing; used by the chem package
+nltk==3.6.2                         # Natural language processing; used by the chem package
 numpy==1.16.5                       # Numeric array processing utilities; used by scipy
 openedx-calc<2.0.0
 pyparsing==2.2.0                    # Python Parsing module
diff --git a/requirements/edx-sandbox/py35.txt b/requirements/edx-sandbox/py35.txt
index cc73253ce7a7..2168f0b7bf22 100644
--- a/requirements/edx-sandbox/py35.txt
+++ b/requirements/edx-sandbox/py35.txt
@@ -51,7 +51,7 @@ networkx==2.2
     # via
     #   -c requirements/edx-sandbox/../constraints.txt
     #   -r requirements/edx-sandbox/py35.in
-nltk==3.6.5
+nltk==3.6.2
     # via
     #   -r requirements/edx-sandbox/py35.in
     #   chem