diff --git a/pandas/src/algos_common_helper.pxi.in b/pandas/src/algos_common_helper.pxi.in
index a579a5020f6e7..5e87528943005 100644
--- a/pandas/src/algos_common_helper.pxi.in
+++ b/pandas/src/algos_common_helper.pxi.in
@@ -374,7 +374,7 @@ def is_monotonic_{{name}}(ndarray[{{c_type}}] arr, bint timelike):
     n = len(arr)
 
     if n == 1:
-        if arr[0] != arr[0] or (timelike and arr[0] == iNaT):
+        if arr[0] != arr[0] or (timelike and <int64_t>arr[0] == iNaT):
             # single value is NaN
             return False, False, True
         else:
@@ -382,14 +382,14 @@ def is_monotonic_{{name}}(ndarray[{{c_type}}] arr, bint timelike):
     elif n < 2:
         return True, True, True
 
-    if timelike and arr[0] == iNaT:
+    if timelike and <int64_t>arr[0] == iNaT:
         return False, False, True
 
     {{nogil_str}}
     {{tab}}prev = arr[0]
     {{tab}}for i in range(1, n):
     {{tab}}    cur = arr[i]
-    {{tab}}    if timelike and cur == iNaT:
+    {{tab}}    if timelike and <int64_t>cur == iNaT:
     {{tab}}        is_monotonic_inc = 0
     {{tab}}        is_monotonic_dec = 0
     {{tab}}        break
diff --git a/pandas/src/algos_groupby_helper.pxi.in b/pandas/src/algos_groupby_helper.pxi.in
index 70862e198edba..4b031afed3d43 100644
--- a/pandas/src/algos_groupby_helper.pxi.in
+++ b/pandas/src/algos_groupby_helper.pxi.in
@@ -580,7 +580,7 @@ def group_cummin_{{name}}(ndarray[{{dest_type2}}, ndim=2] out,
     """
     cdef:
         Py_ssize_t i, j, N, K, size
-        {{dest_type2}} val, min_val
+        {{dest_type2}} val, min_val = 0
         int64_t lab
 
     N, K = (<object> values).shape
@@ -615,7 +615,7 @@ def group_cummax_{{name}}(ndarray[{{dest_type2}}, ndim=2] out,
     """
     cdef:
         Py_ssize_t i, j, N, K, size
-        {{dest_type2}} val, max_val
+        {{dest_type2}} val, max_val = 0
         int64_t lab
 
     N, K = (<object> values).shape
diff --git a/pandas/src/joins_func_helper.pxi.in b/pandas/src/joins_func_helper.pxi.in
index 486c65368602b..9cca9bba2a197 100644
--- a/pandas/src/joins_func_helper.pxi.in
+++ b/pandas/src/joins_func_helper.pxi.in
@@ -41,8 +41,8 @@ def asof_join_backward_{{on_dtype}}_by_{{by_dtype}}(
         Py_ssize_t left_pos, right_pos, left_size, right_size, found_right_pos
         ndarray[int64_t] left_indexer, right_indexer
         bint has_tolerance = 0
-        {{on_dtype}} tolerance_
-        {{on_dtype}} diff
+        {{on_dtype}} tolerance_ = 0
+        {{on_dtype}} diff = 0
         {{table_type}} hash_table
         {{by_dtype}} by_value
 
@@ -106,8 +106,8 @@ def asof_join_forward_{{on_dtype}}_by_{{by_dtype}}(
         Py_ssize_t left_pos, right_pos, left_size, right_size, found_right_pos
         ndarray[int64_t] left_indexer, right_indexer
         bint has_tolerance = 0
-        {{on_dtype}} tolerance_
-        {{on_dtype}} diff
+        {{on_dtype}} tolerance_ = 0
+        {{on_dtype}} diff = 0
         {{table_type}} hash_table
         {{by_dtype}} by_value
 
@@ -236,8 +236,8 @@ def asof_join_backward_{{on_dtype}}(
         Py_ssize_t left_pos, right_pos, left_size, right_size
         ndarray[int64_t] left_indexer, right_indexer
         bint has_tolerance = 0
-        {{on_dtype}} tolerance_
-        {{on_dtype}} diff
+        {{on_dtype}} tolerance_ = 0
+        {{on_dtype}} diff = 0
 
     # if we are using tolerance, set our objects
     if tolerance is not None:
@@ -290,8 +290,8 @@ def asof_join_forward_{{on_dtype}}(
         Py_ssize_t left_pos, right_pos, left_size, right_size
         ndarray[int64_t] left_indexer, right_indexer
         bint has_tolerance = 0
-        {{on_dtype}} tolerance_
-        {{on_dtype}} diff
+        {{on_dtype}} tolerance_ = 0
+        {{on_dtype}} diff = 0
 
     # if we are using tolerance, set our objects
     if tolerance is not None:
@@ -371,4 +371,3 @@ def asof_join_nearest_{{on_dtype}}(
     return left_indexer, right_indexer
 
 {{endfor}}
-