diff --git a/include/asm/format.h b/include/asm/format.h
index 15b2fb48..b9042844 100644
--- a/include/asm/format.h
+++ b/include/asm/format.h
@@ -28,9 +28,9 @@ struct FormatSpec {
 	bool prefix;
 	bool alignLeft;
 	bool padZero;
-	uint8_t width;
+	size_t width;
 	bool hasFrac;
-	uint8_t fracWidth;
+	size_t fracWidth;
 	int type;
 	bool valid;
 };
diff --git a/src/asm/format.c b/src/asm/format.c
index 456cfc25..31572c94 100644
--- a/src/asm/format.c
+++ b/src/asm/format.c
@@ -147,21 +147,25 @@ void fmt_PrintString(char *buf, size_t bufLen, struct FormatSpec const *fmt, cha
 
 	size_t len = strlen(value);
 	size_t totalLen = fmt->width > len ? fmt->width : len;
-
-	if (totalLen + 1 > bufLen) /* bufLen includes terminator */
-		error("Formatted string value too long\n");
-
 	size_t padLen = fmt->width > len ? fmt->width - len : 0;
 
+	if (totalLen + 1 > bufLen) { /* bufLen includes terminator */
+		error("Formatted string value too long\n");
+		totalLen = bufLen - 1;
+		if (len > totalLen)
+			len = totalLen;
+		padLen = totalLen - len;
+	}
+
 	if (fmt->alignLeft) {
-		strncpy(buf, value, len < bufLen ? len : bufLen);
+		memcpy(buf, value, len < bufLen ? len : bufLen);
 		for (size_t i = 0; i < totalLen && len + i < bufLen; i++)
 			buf[len + i] = ' ';
 	} else {
 		for (size_t i = 0; i < padLen && i < bufLen; i++)
 			buf[i] = ' ';
 		if (bufLen > padLen)
-			strncpy(buf + padLen, value, bufLen - padLen - 1);
+			memcpy(buf + padLen, value, bufLen - padLen - 1);
 	}
 
 	buf[totalLen] = '\0';
@@ -221,12 +225,18 @@ void fmt_PrintNumber(char *buf, size_t bufLen, struct FormatSpec const *fmt, uin
 		/* Special case for fixed-point */
 
 		/* Default fractional width (C's is 6 for "%f"; here 5 is enough) */
-		uint8_t fracWidth = fmt->hasFrac ? fmt->fracWidth : 5;
+		size_t fracWidth = fmt->hasFrac ? fmt->fracWidth : 5;
 
 		if (fracWidth) {
+			if (fracWidth > 255) {
+				error("Fractional width %zu too long, limiting to 255\n",
+				       fracWidth);
+				fracWidth = 255;
+			}
+
 			char spec[16]; /* Max "%" + 5-char PRIu32 + ".%0255.f" + terminator */
 
-			snprintf(spec, sizeof(spec), "%%" PRIu32 ".%%0%d.f", fracWidth);
+			snprintf(spec, sizeof(spec), "%%" PRIu32 ".%%0%zu.f", fracWidth);
 			snprintf(valueBuf, sizeof(valueBuf), spec, value >> 16,
 				 (value % 65536) / 65536.0 * pow(10, fracWidth) + 0.5);
 		} else {
@@ -252,12 +262,18 @@ void fmt_PrintNumber(char *buf, size_t bufLen, struct FormatSpec const *fmt, uin
 		numLen++;
 
 	size_t totalLen = fmt->width > numLen ? fmt->width : numLen;
-
-	if (totalLen + 1 > bufLen) /* bufLen includes terminator */
-		error("Formatted numeric value too long\n");
-
 	size_t padLen = fmt->width > numLen ? fmt->width - numLen : 0;
 
+	if (totalLen + 1 > bufLen) { /* bufLen includes terminator */
+		error("Formatted numeric value too long\n");
+		totalLen = bufLen - 1;
+		if (numLen > totalLen) {
+			len = totalLen - (numLen - len);
+			numLen = totalLen;
+		}
+		padLen = totalLen - numLen;
+	}
+
 	if (fmt->alignLeft) {
 		size_t pos = 0;
 
diff --git a/src/asm/rgbasm.5 b/src/asm/rgbasm.5
index 10e92028..2371e62f 100644
--- a/src/asm/rgbasm.5
+++ b/src/asm/rgbasm.5
@@ -337,7 +337,7 @@ followed by one or more
 \[en]
 .Ql 9 .
 If specified, prints this many digits of a fixed-point fraction.
-Defaults to 5 digits.
+Defaults to 5 digits, maximum 255 digits.
 .It Ql <type> Ta Specifies the type of value.
 .El
 .Pp
diff --git a/test/asm/format-truncation.asm b/test/asm/format-truncation.asm
new file mode 100644
index 00000000..cc7cff9a
--- /dev/null
+++ b/test/asm/format-truncation.asm
@@ -0,0 +1,15 @@
+num equ 42
+fix equ 123.456
+str equs "hello"
+
+println "{#0260x:num}"
+println "{#-260x:num}"
+println "{0280.260f:fix}"
+println "{260s:str}"
+println "{-260s:str}"
+
+println "<{#0260x:num}>"
+println "<{#-260x:num}>"
+println "<{0280.260f:fix}>"
+println "<{260s:str}>"
+println "<{-260s:str}>"
diff --git a/test/asm/format-truncation.err b/test/asm/format-truncation.err
new file mode 100644
index 00000000..01ee8689
--- /dev/null
+++ b/test/asm/format-truncation.err
@@ -0,0 +1,35 @@
+ERROR: format-truncation.asm(5):
+    Formatted numeric value too long
+ERROR: format-truncation.asm(6):
+    Formatted numeric value too long
+ERROR: format-truncation.asm(7):
+    Fractional width 260 too long, limiting to 255
+ERROR: format-truncation.asm(7):
+    Formatted numeric value too long
+ERROR: format-truncation.asm(8):
+    Formatted string value too long
+ERROR: format-truncation.asm(9):
+    Formatted string value too long
+ERROR: format-truncation.asm(11):
+    Formatted numeric value too long
+warning: format-truncation.asm(11): [-Wlong-string]
+    String constant too long
+ERROR: format-truncation.asm(12):
+    Formatted numeric value too long
+warning: format-truncation.asm(12): [-Wlong-string]
+    String constant too long
+ERROR: format-truncation.asm(13):
+    Fractional width 260 too long, limiting to 255
+ERROR: format-truncation.asm(13):
+    Formatted numeric value too long
+warning: format-truncation.asm(13): [-Wlong-string]
+    String constant too long
+ERROR: format-truncation.asm(14):
+    Formatted string value too long
+warning: format-truncation.asm(14): [-Wlong-string]
+    String constant too long
+ERROR: format-truncation.asm(15):
+    Formatted string value too long
+warning: format-truncation.asm(15): [-Wlong-string]
+    String constant too long
+error: Assembly aborted (12 errors)!
diff --git a/test/asm/format-truncation.out b/test/asm/format-truncation.out
new file mode 100644
index 00000000..5713af55
--- /dev/null
+++ b/test/asm/format-truncation.out
@@ -0,0 +1,10 @@
+$0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002a
+$2a                                                                                                                                                                                                                                                            
+123.45599365234375001369732334415661667551799560000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+                                                                                                                                                                                                                                                          hello
+hello                                                                                                                                                                                                                                                          
+<$0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002
+<$2a                                                                                                                                                                                                                                                           
+<123.4559936523437500136973233441566166755179956000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+<                                                                                                                                                                                                                                                          hell
+<hello                                                                                                                                                                                                                                                         
diff --git a/test/asm/interpolation-overflow.asm b/test/asm/interpolation-overflow.asm
new file mode 100644
index 00000000..aa781380
--- /dev/null
+++ b/test/asm/interpolation-overflow.asm
@@ -0,0 +1,4 @@
+; It seems that \1 was the easiest way to notice the memory corruption that
+; resulted from this overflow
+x = 0
+{.99999999f:x}\1
diff --git a/test/asm/interpolation-overflow.err b/test/asm/interpolation-overflow.err
new file mode 100644
index 00000000..1d70758f
--- /dev/null
+++ b/test/asm/interpolation-overflow.err
@@ -0,0 +1,9 @@
+ERROR: interpolation-overflow.asm(4):
+    Fractional width 99999999 too long, limiting to 255
+ERROR: interpolation-overflow.asm(4):
+    Formatted numeric value too long
+warning: interpolation-overflow.asm(4): [-Wlarge-constant]
+    Precision of fixed-point constant is too large
+while expanding symbol "0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
+FATAL: interpolation-overflow.asm(4):
+    Macro argument '\1' not defined
diff --git a/test/asm/interpolation-overflow.out b/test/asm/interpolation-overflow.out
new file mode 100644
index 00000000..e69de29b