diff --git a/integration_tests/data/cross_db/data_datediff.csv b/integration_tests/data/cross_db/data_datediff.csv
index 5d266969..57b0da4e 100644
--- a/integration_tests/data/cross_db/data_datediff.csv
+++ b/integration_tests/data/cross_db/data_datediff.csv
@@ -3,5 +3,11 @@ first_date,second_date,datepart,result
 2018-01-01 01:00:00,2018-02-01 01:00:00,month,1
 2018-01-01 01:00:00,2019-01-01 01:00:00,year,1
 2018-01-01 01:00:00,2018-01-01 02:00:00,hour,1
+2018-01-01 01:00:00,2018-01-01 02:01:00,minute,61
+2018-01-01 01:00:00,2018-01-01 02:00:01,second,3601
+2019-12-31 00:00:00,2019-12-27 00:00:00,week,-1
+2019-12-31 00:00:00,2019-12-30 00:00:00,week,0
+2019-12-31 00:00:00,2020-01-02 00:00:00,week,0
+2019-12-31 00:00:00,2020-01-06 02:00:00,week,1
 ,2018-01-01 02:00:00,hour,
 2018-01-01 02:00:00,,hour,
diff --git a/integration_tests/models/cross_db_utils/test_datediff.sql b/integration_tests/models/cross_db_utils/test_datediff.sql
index acb7c217..a2340456 100644
--- a/integration_tests/models/cross_db_utils/test_datediff.sql
+++ b/integration_tests/models/cross_db_utils/test_datediff.sql
@@ -6,19 +6,30 @@ with data as (
 )
 
 select
-    -- not implemented for postgres
-    {% if target.type == 'postgres' %}
-        null::text as actual,
-        null::text as expected
-    {% else %}
-        case
-            when datepart = 'hour' then {{ dbt_utils.datediff('first_date', 'second_date', 'hour') }}
-            when datepart = 'day' then {{ dbt_utils.datediff('first_date', 'second_date', 'day') }}
-            when datepart = 'month' then {{ dbt_utils.datediff('first_date', 'second_date', 'month') }}
-            when datepart = 'year' then {{ dbt_utils.datediff('first_date', 'second_date', 'year') }}
-            else null
-        end as actual,
-        result as expected
-    {% endif %}
+
+    case
+        when datepart = 'second' then {{ dbt_utils.datediff('first_date', 'second_date', 'second') }}
+        when datepart = 'minute' then {{ dbt_utils.datediff('first_date', 'second_date', 'minute') }}
+        when datepart = 'hour' then {{ dbt_utils.datediff('first_date', 'second_date', 'hour') }}
+        when datepart = 'day' then {{ dbt_utils.datediff('first_date', 'second_date', 'day') }}
+        when datepart = 'week' then {{ dbt_utils.datediff('first_date', 'second_date', 'week') }}
+        when datepart = 'month' then {{ dbt_utils.datediff('first_date', 'second_date', 'month') }}
+        when datepart = 'year' then {{ dbt_utils.datediff('first_date', 'second_date', 'year') }}
+        else null
+    end as actual,
+    result as expected
 
 from data
+
+-- Also test correct casting of literal values.
+
+union all select {{ dbt_utils.datediff("'1999-12-31 23:59:59.999999'", "'2000-01-01 00:00:00.000000'", "microsecond") }} as actual, 1 as expected
+union all select {{ dbt_utils.datediff("'1999-12-31 23:59:59.999999'", "'2000-01-01 00:00:00.000000'", "millisecond") }} as actual, 1 as expected
+union all select {{ dbt_utils.datediff("'1999-12-31 23:59:59.999999'", "'2000-01-01 00:00:00.000000'", "second") }} as actual, 1 as expected
+union all select {{ dbt_utils.datediff("'1999-12-31 23:59:59.999999'", "'2000-01-01 00:00:00.000000'", "minute") }} as actual, 1 as expected
+union all select {{ dbt_utils.datediff("'1999-12-31 23:59:59.999999'", "'2000-01-01 00:00:00.000000'", "hour") }} as actual, 1 as expected
+union all select {{ dbt_utils.datediff("'1999-12-31 23:59:59.999999'", "'2000-01-01 00:00:00.000000'", "day") }} as actual, 1 as expected
+union all select {{ dbt_utils.datediff("'1999-12-31 23:59:59.999999'", "'2000-01-03 00:00:00.000000'", "week") }} as actual, 1 as expected
+union all select {{ dbt_utils.datediff("'1999-12-31 23:59:59.999999'", "'2000-01-01 00:00:00.000000'", "month") }} as actual, 1 as expected
+union all select {{ dbt_utils.datediff("'1999-12-31 23:59:59.999999'", "'2000-01-01 00:00:00.000000'", "quarter") }} as actual, 1 as expected
+union all select {{ dbt_utils.datediff("'1999-12-31 23:59:59.999999'", "'2000-01-01 00:00:00.000000'", "year") }} as actual, 1 as expected
diff --git a/macros/cross_db_utils/datediff.sql b/macros/cross_db_utils/datediff.sql
index 546a7a62..c0c1e7d4 100644
--- a/macros/cross_db_utils/datediff.sql
+++ b/macros/cross_db_utils/datediff.sql
@@ -20,13 +20,40 @@
         cast({{second_date}} as datetime),
         cast({{first_date}} as datetime),
         {{datepart}}
-    ) 
+    )
 
 {% endmacro %}
 
 
 {% macro postgres__datediff(first_date, second_date, datepart) %}
 
-    {{ exceptions.raise_compiler_error("macro datediff not implemented for this adapter") }}
+    {% if datepart == 'year' %}
+        (date_part('year', ({{second_date}})::date) - date_part('year', ({{first_date}})::date))
+    {% elif datepart == 'quarter' %}
+        ({{ dbt_utils.datediff(first_date, second_date, 'year') }} * 4 + date_part('quarter', ({{second_date}})::date) - date_part('quarter', ({{first_date}})::date))
+    {% elif datepart == 'month' %}
+        ({{ dbt_utils.datediff(first_date, second_date, 'year') }} * 12 + date_part('month', ({{second_date}})::date) - date_part('month', ({{first_date}})::date))
+    {% elif datepart == 'day' %}
+        (({{second_date}})::date - ({{first_date}})::date)
+    {% elif datepart == 'week' %}
+        ({{ dbt_utils.datediff(first_date, second_date, 'day') }} / 7 + case
+            when date_part('dow', ({{first_date}})::timestamp) <= date_part('dow', ({{second_date}})::timestamp) then
+                case when {{first_date}} <= {{second_date}} then 0 else -1 end
+            else
+                case when {{first_date}} <= {{second_date}} then 1 else 0 end
+        end)
+    {% elif datepart == 'hour' %}
+        ({{ dbt_utils.datediff(first_date, second_date, 'day') }} * 24 + date_part('hour', ({{second_date}})::timestamp) - date_part('hour', ({{first_date}})::timestamp))
+    {% elif datepart == 'minute' %}
+        ({{ dbt_utils.datediff(first_date, second_date, 'hour') }} * 60 + date_part('minute', ({{second_date}})::timestamp) - date_part('minute', ({{first_date}})::timestamp))
+    {% elif datepart == 'second' %}
+        ({{ dbt_utils.datediff(first_date, second_date, 'minute') }} * 60 + floor(date_part('second', ({{second_date}})::timestamp)) - floor(date_part('second', ({{first_date}})::timestamp)))
+    {% elif datepart == 'millisecond' %}
+        ({{ dbt_utils.datediff(first_date, second_date, 'minute') }} * 60000 + floor(date_part('millisecond', ({{second_date}})::timestamp)) - floor(date_part('millisecond', ({{first_date}})::timestamp)))
+    {% elif datepart == 'microsecond' %}
+        ({{ dbt_utils.datediff(first_date, second_date, 'minute') }} * 60000000 + floor(date_part('microsecond', ({{second_date}})::timestamp)) - floor(date_part('microsecond', ({{first_date}})::timestamp)))
+    {% else %}
+        {{ exceptions.raise_compiler_error("Unsupported datepart for macro datediff in postgres: {!r}".format(datepart)) }}
+    {% endif %}
 
 {% endmacro %}