diff --git a/src/apfl.h b/src/apfl.h
index 20df27c..8eee50a 100644
--- a/src/apfl.h
+++ b/src/apfl.h
@@ -40,8 +40,8 @@ struct apfl_allocator apfl_allocator_wrap_verifying(struct apfl_allocator *wrapp
 typedef double apfl_number;
 
 struct apfl_position {
-    int line;
-    int col;
+    size_t line;
+    size_t col;
 };
 
 bool apfl_position_eq(struct apfl_position, struct apfl_position);
@@ -749,8 +749,8 @@ struct apfl_call_stack_entry_info {
     size_t subfunction_index; // Only set for type==APFL_CSE_FUNCTION && !toplevel
     struct apfl_string_view filename;
     struct apfl_string_view name;
-    int line_current; // only set for (type==APFL_CSE_FUNCTION && !toplevel) || type == APFL_CSE_FUNCTION_DISPATCH
-    int line_defined; // only set for type==APFL_CSE_FUNCTION
+    size_t line_current; // only set for (type==APFL_CSE_FUNCTION && !toplevel) || type == APFL_CSE_FUNCTION_DISPATCH
+    size_t line_defined; // only set for type==APFL_CSE_FUNCTION
 };
 
 // Get the depth of the current call stack
diff --git a/src/bytecode.c b/src/bytecode.c
index b5cbbbd..3459f05 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -8,7 +8,7 @@
 #include "gc.h"
 
 struct instruction_list *
-apfl_instructions_new(struct gc *gc, int line, struct apfl_string *filename)
+apfl_instructions_new(struct gc *gc, size_t line, struct apfl_string *filename)
 {
     struct instruction_list *ilist = apfl_gc_new_instructions(gc);
     if (ilist == NULL) {
diff --git a/src/bytecode.h b/src/bytecode.h
index d005a39..5d47bd4 100644
--- a/src/bytecode.h
+++ b/src/bytecode.h
@@ -85,14 +85,14 @@ struct instruction_list {
     size_t len;
     size_t cap;
 
-    int line;
+    size_t line;
     struct apfl_string *filename;
 };
 
 const char *apfl_instruction_to_string(enum instruction);
 const char *apfl_matcher_instruction_to_string(enum matcher_instruction);
 
-struct instruction_list *apfl_instructions_new(struct gc *, int line, struct apfl_string *filename);
+struct instruction_list *apfl_instructions_new(struct gc *, size_t line, struct apfl_string *filename);
 void apfl_instructions_deinit(struct apfl_allocator, struct instruction_list *);
 
 void apfl_gc_instructions_traverse(struct instruction_list *, gc_visitor, void *);
diff --git a/src/compile.c b/src/compile.c
index d0cef4c..bf4d46b 100644
--- a/src/compile.c
+++ b/src/compile.c
@@ -296,7 +296,7 @@ compile_simple_assignment(
 }
 
 static struct instruction_list *
-tmp_ilist(struct compiler *compiler, int line, struct apfl_string *filename)
+tmp_ilist(struct compiler *compiler, size_t line, struct apfl_string *filename)
 {
     struct instruction_list *ilist;
     if (
diff --git a/src/context.c b/src/context.c
index 709e186..0c68a80 100644
--- a/src/context.c
+++ b/src/context.c
@@ -1976,7 +1976,7 @@ format_defined_at(
         FMT_TRY(apfl_io_write_string(w, ", "));
     }
     FMT_TRY(apfl_io_write_string(w, "line "));
-    FMT_TRY(apfl_format_put_int(w, info.line_defined));
+    FMT_TRY(apfl_format_put_int(w, (int)info.line_defined));
     return true;
 }
 
@@ -1991,7 +1991,7 @@ apfl_call_stack_entry_info_format(struct apfl_io_writer w, struct apfl_call_stac
             FMT_TRY(apfl_io_write_string(w, ", "));
         }
         FMT_TRY(apfl_io_write_string(w, "Line "));
-        FMT_TRY(apfl_format_put_int(w, info.line_current));
+        FMT_TRY(apfl_format_put_int(w, (int)info.line_current));
         FMT_TRY(apfl_io_write_string(w, ", "));
 
         if (info.toplevel) {
diff --git a/src/context.h b/src/context.h
index b03af2a..fe258e8 100644
--- a/src/context.h
+++ b/src/context.h
@@ -54,7 +54,7 @@ struct func_call_stack_entry {
     // scopes.scope will be created lazily
     struct scopes scopes;
 
-    int execution_line;
+    size_t execution_line;
 
     struct function *function; // Can be NULL, in that case it's the toplevel
     size_t subfunction_index; // Not set, if function == NULL
diff --git a/src/error.c b/src/error.c
index 4b52116..cb1b0ac 100644
--- a/src/error.c
+++ b/src/error.c
@@ -1,12 +1,13 @@
+#include <inttypes.h>
 #include <stdio.h>
 
 #include "apfl.h"
 
 #include "format.h"
 
-#define POSFMT "%d:%d"
-#define POSARGS error.position.line, error.position.col
-#define POS2ARGS error.position2.line, error.position2.col
+#define POSFMT "%" PRIuMAX ":%" PRIuMAX
+#define POSARGS (umaxint_t)error.position.line, (umaxint_t)error.position.col
+#define POS2ARGS (umaxint_t)error.position2.line, (umaxint_t)error.position2.col
 
 #define TRY(x) do { if (!(x)) return false; } while (0)
 
diff --git a/src/format.c b/src/format.c
index 855de7e..bd2080c 100644
--- a/src/format.c
+++ b/src/format.c
@@ -86,9 +86,9 @@ apfl_format_put_hexbyte(struct apfl_io_writer w, unsigned char c)
 bool
 apfl_format_put_pos(struct apfl_io_writer w, struct apfl_position pos)
 {
-    TRY(apfl_format_put_int(w, pos.line));
+    TRY(apfl_format_put_int(w, (int)pos.line));
     TRY(apfl_io_write_string(w, ":"));
-    TRY(apfl_format_put_int(w, pos.col));
+    TRY(apfl_format_put_int(w, (int)pos.col));
     return true;
 }
 
diff --git a/src/parser_test.c b/src/parser_test.c
index 5a69899..b630e73 100644
--- a/src/parser_test.c
+++ b/src/parser_test.c
@@ -237,7 +237,7 @@ MKLISTBUILDER(assignable_list, struct apfl_expr_assignable_list, struct apfl_exp
 #define POS(l, c) (struct apfl_position) { .line = l, .col = c }
 
 static struct apfl_expr
-var(struct parser_test *pt, int line, int col, const char *v)
+var(struct parser_test *pt, size_t line, size_t col, const char *v)
 {
     return (struct apfl_expr) {
         .type = APFL_EXPR_VAR,
@@ -247,14 +247,14 @@ var(struct parser_test *pt, int line, int col, const char *v)
 }
 
 struct apfl_expr *
-new_var(struct parser_test *pt, int line, int col, const char *v)
+new_var(struct parser_test *pt, size_t line, size_t col, const char *v)
 {
     struct apfl_expr expr = var(pt, line, col, v);
     return new_helper(pt, sizeof(struct apfl_expr), &expr);
 }
 
 static struct apfl_expr
-dot(struct parser_test *pt, int line, int col, const char *rhs, struct apfl_expr *lhs)
+dot(struct parser_test *pt, size_t line, size_t col, const char *rhs, struct apfl_expr *lhs)
 {
     return (struct apfl_expr) {
         .type = APFL_EXPR_DOT,
@@ -265,7 +265,7 @@ dot(struct parser_test *pt, int line, int col, const char *rhs, struct apfl_expr
 }
 
 static struct apfl_expr *
-new_dot(struct parser_test *pt, int line, int col, const char *rhs, struct apfl_expr *lhs)
+new_dot(struct parser_test *pt, size_t line, size_t col, const char *rhs, struct apfl_expr *lhs)
 {
     struct apfl_expr expr = dot(pt, line, col, rhs, lhs);
     return new_helper(pt, sizeof(struct apfl_expr), &expr);
@@ -300,7 +300,7 @@ bool_const(bool b)
 }
 
 static struct apfl_expr
-const_expr(int line, int col, struct apfl_expr_const constant)
+const_expr(size_t line, size_t col, struct apfl_expr_const constant)
 {
     return (struct apfl_expr) {
         .type = APFL_EXPR_CONSTANT,
@@ -310,7 +310,7 @@ const_expr(int line, int col, struct apfl_expr_const constant)
 }
 
 static struct apfl_expr *
-new_const_expr(struct parser_test *pt, int line, int col, struct apfl_expr_const constant)
+new_const_expr(struct parser_test *pt, size_t line, size_t col, struct apfl_expr_const constant)
 {
     struct apfl_expr expr = const_expr(line, col, constant);
     return new_helper(pt, sizeof(struct apfl_expr), &expr);
diff --git a/src/token.c b/src/token.c
index 72e2aa9..1485354 100644
--- a/src/token.c
+++ b/src/token.c
@@ -1,3 +1,4 @@
+#include <inttypes.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -95,28 +96,28 @@ apfl_token_print(struct apfl_token token, FILE *file)
     if (has_text_data(token.type)) {
         fprintf(
             file,
-            "%s (" APFL_STR_FMT ") @ (%d:%d)\n",
+            "%s (" APFL_STR_FMT ") @ (%" PRIuMAX ":%" PRIuMAX ")\n",
             apfl_token_type_name(token.type),
             APFL_STR_FMT_ARGS(apfl_string_view_from(token.text)),
-            token.position.line,
-            token.position.col
+            (uintmax_t)token.position.line,
+            (uintmax_t)token.position.col
         );
     } else if (has_numeric_data(token.type)) {
         fprintf(
             file,
-            "%s (%f) @ (%d:%d)\n",
+            "%s (%f) @ (%" PRIuMAX ":%" PRIuMAX ")\n",
             apfl_token_type_name(token.type),
             token.number,
-            token.position.line,
-            token.position.col
+            (uintmax_t)token.position.line,
+            (uintmax_t)token.position.col
         );
     } else {
         fprintf(
             file,
-            "%s @ (%d:%d)\n",
+            "%s @ (%" PRIuMAX ":%" PRIuMAX ")\n",
             apfl_token_type_name(token.type),
-            token.position.line,
-            token.position.col
+            (uintmax_t)token.position.line,
+            (uintmax_t)token.position.col
         );
     }
 }
diff --git a/src/tokenizer_test.c b/src/tokenizer_test.c
index 0d97511..9b62aa1 100644
--- a/src/tokenizer_test.c
+++ b/src/tokenizer_test.c
@@ -1,4 +1,5 @@
 #include <assert.h>
+#include <inttypes.h>
 
 #include "apfl.h"
 
@@ -65,7 +66,7 @@ expect_eof(struct tokenizer_test *tt)
 }
 
 static bool
-expect_token(struct tokenizer_test *tt, int line, int col, enum apfl_token_type type, struct apfl_token *tok)
+expect_token(struct tokenizer_test *tt, size_t line, size_t col, enum apfl_token_type type, struct apfl_token *tok)
 {
     switch (apfl_tokenizer_next(tt->tokenizer, false)) {
     case APFL_PARSE_OK:
@@ -94,14 +95,23 @@ expect_token(struct tokenizer_test *tt, int line, int col, enum apfl_token_type
     }
 
     if (tok->position.line != line || tok->position.col != col) {
-        test_failf(tt->t, "Got token at wrong position %d:%d (wanted %d:%d)", tok->position.line, tok->position.col, line, col);
+        test_failf(
+            tt->t,
+            "Got token at wrong position %" PRIuMAX ":%" PRIuMAX
+            " (wanted %" PRIuMAX ":%" PRIuMAX ")",
+
+            (uintmax_t)tok->position.line,
+            (uintmax_t)tok->position.col,
+            (uintmax_t)line,
+            (uintmax_t)col
+        );
     }
 
     return true;
 }
 
 static void
-expect_simple_token(struct tokenizer_test *tt, int line, int col, enum apfl_token_type type)
+expect_simple_token(struct tokenizer_test *tt, size_t line, size_t col, enum apfl_token_type type)
 {
     struct apfl_token tok;
     if (expect_token(tt, line, col, type, &tok)) {
@@ -110,7 +120,7 @@ expect_simple_token(struct tokenizer_test *tt, int line, int col, enum apfl_toke
 }
 
 static void
-expect_text_token(struct tokenizer_test *tt, int line, int col, enum apfl_token_type type, const char *text)
+expect_text_token(struct tokenizer_test *tt, size_t line, size_t col, enum apfl_token_type type, const char *text)
 {
     struct apfl_token tok;
     if (expect_token(tt, line, col, type, &tok)) {
@@ -123,7 +133,7 @@ expect_text_token(struct tokenizer_test *tt, int line, int col, enum apfl_token_
 }
 
 static void
-expect_text_token_sv(struct tokenizer_test *tt, int line, int col, enum apfl_token_type type, struct apfl_string_view text)
+expect_text_token_sv(struct tokenizer_test *tt, size_t line, size_t col, enum apfl_token_type type, struct apfl_string_view text)
 {
     struct apfl_token tok;
     if (expect_token(tt, line, col, type, &tok)) {
@@ -136,7 +146,7 @@ expect_text_token_sv(struct tokenizer_test *tt, int line, int col, enum apfl_tok
 }
 
 static void
-expect_number_token(struct tokenizer_test *tt, int line, int col, enum apfl_token_type type, apfl_number num)
+expect_number_token(struct tokenizer_test *tt, size_t line, size_t col, enum apfl_token_type type, apfl_number num)
 {
     struct apfl_token tok;
     if (expect_token(tt, line, col, type, &tok)) {