diff --git a/luna/src/NumberParsing.cpp b/luna/src/NumberParsing.cpp
index 1f4c7680..0938c06b 100644
--- a/luna/src/NumberParsing.cpp
+++ b/luna/src/NumberParsing.cpp
@@ -1,3 +1,4 @@
+#include <limits.h>
 #include <luna/CType.h>
 #include <luna/NumberParsing.h>
 
@@ -47,6 +48,9 @@ usize parse_unsigned_integer(const char* str, const char** endptr, int base)
     return val;
 }
 
+#define SSIZE_MAX LONG_MAX
+#define SSIZE_MIN (-SSIZE_MAX - (isize)1)
+
 isize parse_signed_integer(const char* str, const char** endptr, int base)
 {
     bool negative = false;
@@ -59,9 +63,9 @@ isize parse_signed_integer(const char* str, const char** endptr, int base)
         str++;
     }
 
-    usize rc = parse_unsigned_integer(
-        str, endptr,
-        base); // FIXME: Check for overflow (the unsigned usize value might not fit into a signed isize)
+    usize rc = parse_unsigned_integer(str, endptr, base);
+
+    if (rc > SSIZE_MAX) { return negative ? SSIZE_MIN : SSIZE_MAX; }
 
     return negative ? -(isize)rc : (isize)rc;
 }