diff --git a/pandas/_libs/src/parse_helper.h b/pandas/_libs/src/parse_helper.h
index 0a767dd27b658..7fbe7a04d5b22 100644
--- a/pandas/_libs/src/parse_helper.h
+++ b/pandas/_libs/src/parse_helper.h
@@ -11,8 +11,6 @@ The full license is in the LICENSE file, distributed with this software.
 #define PANDAS__LIBS_SRC_PARSE_HELPER_H_
 
 #include <float.h>
-#include "inline_helper.h"
-#include "headers/portable.h"
 #include "parser/tokenizer.h"
 
 int to_double(char *item, double *p_value, char sci, char decimal,
@@ -94,12 +92,4 @@ int floatify(PyObject *str, double *result, int *maybe_int) {
     return -1;
 }
 
-PANDAS_INLINE void lowercase(char *p) {
-    for (; *p; ++p) *p = tolower_ascii(*p);
-}
-
-PANDAS_INLINE void uppercase(char *p) {
-    for (; *p; ++p) *p = toupper_ascii(*p);
-}
-
 #endif  // PANDAS__LIBS_SRC_PARSE_HELPER_H_
diff --git a/pandas/_libs/src/parser/tokenizer.c b/pandas/_libs/src/parser/tokenizer.c
index 2752fb6424022..83869a1d9c342 100644
--- a/pandas/_libs/src/parser/tokenizer.c
+++ b/pandas/_libs/src/parser/tokenizer.c
@@ -1426,42 +1426,30 @@ int tokenize_all_rows(parser_t *self) {
     return status;
 }
 
-PANDAS_INLINE void uppercase(char *p) {
-    for (; *p; ++p) *p = toupper_ascii(*p);
-}
-
+/*
+ * Function: to_boolean
+ * --------------------
+ *
+ * Validate if item should be recognized as a boolean field.
+ *
+ * item: const char* representing parsed text
+ * val : pointer to a uint8_t of boolean representation
+ *
+ * If item is determined to be boolean, this method will set
+ * the appropriate value of val and return 0. A non-zero exit
+ * status means that item was not inferred to be boolean, and
+ * leaves the value of *val unmodified.
+ */
 int to_boolean(const char *item, uint8_t *val) {
-    char *tmp;
-    int i, status = 0;
-    size_t length0 = (strlen(item) + 1);
-    int bufsize = length0;
-
-    static const char *tstrs[1] = {"TRUE"};
-    static const char *fstrs[1] = {"FALSE"};
-
-    tmp = malloc(bufsize);
-    snprintf(tmp,  length0, "%s", item);
-    uppercase(tmp);
-
-    for (i = 0; i < 1; ++i) {
-        if (strcmp(tmp, tstrs[i]) == 0) {
-            *val = 1;
-            goto done;
-        }
+    if (strcasecmp(item, "TRUE") == 0) {
+      *val = 1;
+      return 0;
+    } else if (strcasecmp(item, "FALSE") == 0) {
+      *val = 0;
+      return 0;
     }
 
-    for (i = 0; i < 1; ++i) {
-        if (strcmp(tmp, fstrs[i]) == 0) {
-            *val = 0;
-            goto done;
-        }
-    }
-
-    status = -1;
-
-done:
-    free(tmp);
-    return status;
+    return -1;
 }
 
 // ---------------------------------------------------------------------------
diff --git a/pandas/_libs/src/parser/tokenizer.h b/pandas/_libs/src/parser/tokenizer.h
index 66ef1887d6bc3..802b58d8ec916 100644
--- a/pandas/_libs/src/parser/tokenizer.h
+++ b/pandas/_libs/src/parser/tokenizer.h
@@ -22,6 +22,7 @@ See LICENSE for the license
 
 #include "../headers/stdint.h"
 #include "../inline_helper.h"
+#include "../headers/portable.h"
 
 #include "khash.h"