diff --git a/codelists/closed/frequency_distribution.csv b/codelists/closed/frequency_distribution.csv
index 7c4af379..1bbab69a 100644
--- a/codelists/closed/frequency_distribution.csv
+++ b/codelists/closed/frequency_distribution.csv
@@ -1,4 +1,4 @@
 Code,Title,Description
 poisson,Poisson,Data modelled using a poisson distribution.
-negativeBinomial,Negative Binomial,Data modelled using a negative binomial distribution.
-userDefined,User defined,Data modelled using a user defined distribution.
+negative_binomial,Negative Binomial,Data modelled using a negative binomial distribution.
+user_defined,User defined,Data modelled using a user defined distribution.
diff --git a/codelists/closed/seasonality.csv b/codelists/closed/seasonality.csv
index cf0607f0..e2be6232 100644
--- a/codelists/closed/seasonality.csv
+++ b/codelists/closed/seasonality.csv
@@ -1,3 +1,3 @@
 Code,Title
 uniform,Uniform
-userDefined,User defined
+user_defined,User defined
diff --git a/docs/about/changelog.md b/docs/about/changelog.md
index b15b5ef6..338d6d4a 100644
--- a/docs/about/changelog.md
+++ b/docs/about/changelog.md
@@ -61,6 +61,7 @@ This page lists changes to the Risk Data Library Standard.
 - [#121](https://github.com/GFDRR/rdl-standard/pull/121) - Create 'frequency_distribution.csv' and 'seasonality.csv'
 - [#130](https://github.com/GFDRR/rdl-standard/pull/130) - 'hazard_type.csv' add descriptions and hazard category which aligns with UNDRR Hazard taxonomy, and update codes from abbreviations to human-readable words.
 - [#134](https://github.com/GFDRR/rdl-standard/pull/134) - 'risk_data_type.csv', replace codes with lower-case versions.
+- [#164](https://github.com/GFDRR/rdl-standard/pull/164) - replace camelCase codes with snake_case codes in 'frequency_distribution.csv' and 'seasonality.csv'
 
 ### Normative documentation
 
diff --git a/schema/rdl_schema_0.1.json b/schema/rdl_schema_0.1.json
index 3d91ae5e..2726c144 100644
--- a/schema/rdl_schema_0.1.json
+++ b/schema/rdl_schema_0.1.json
@@ -1708,8 +1708,8 @@
           "openCodelist": false,
           "enum": [
             "poisson",
-            "negativeBinomial",
-            "userDefined"
+            "negative_binomial",
+            "user_defined"
           ]
         },
         "seasonality": {
@@ -1720,7 +1720,7 @@
           "openCodelist": false,
           "enum": [
             "uniform",
-            "userDefined"
+            "user_defined"
           ]
         },
         "calculation_method": {